Appendix D1, Modeling Brine Disposal into Monterey Bay ...

CalAm Monterey Peninsula Water Supply Project D1-1 ESA / 205335.01 Final EIR/EIS March 2018

APPENDIX D1 Modeling Brine Disposal into Monterey Bay – Supplement, Final Report

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Modeling Brine Disposal into Monterey Bay –

Supplement

Philip J. W. Roberts, PhD, PE

Consulting Engineer

Atlanta, Georgia, USA

Final Report

Prepared for

ESA | Environmental Science Associates

San Francisco, California

September 22, 2017

i

CONTENTS

Contents ..................................................................................................................................... i

Executive Summary ................................................................................................................. ii

List of Figures .......................................................................................................................... iii

List of Tables ........................................................................................................................... iv

1. Introduction ......................................................................................................................... 1

2. Modeling Scenarios ............................................................................................................ 2 2.1 Introduction ................................................................................................................ 2 2.2 Environmental and Discharge Conditions ................................................................ 2 2.3 Discharge Scenarios ................................................................................................... 3

3. Outfall Hydraulics ................................................................................................................7 3.1 Introduction .................................................................................................................7 3.2 Effect of End Gate Valve on Dilution ........................................................................ 9

4. Dense Discharge Dilution ................................................................................................. 10 4.1 Introduction .............................................................................................................. 10 4.2 Results ....................................................................................................................... 10 4.3 Effect of Currents ...................................................................................................... 14 4.4 Dilution of End Gate Check Valve ............................................................................ 15

5. Buoyant Discharge Dilution .............................................................................................. 17 5.1 Introduction ............................................................................................................... 17 5.2 Results ........................................................................................................................ 17

6. Dilution Mitigation – Effect of Nozzle Angle .................................................................. 20 6.1 Introduction .............................................................................................................. 20 6.2 Dense Effluents ........................................................................................................ 20 6.3 Buoyant Effluents ..................................................................................................... 23

References .............................................................................................................................. 25

Appendix A. Density Profiles ................................................................................................. 26

Appendix B. Additional Scenarios ........................................................................................ 27

Appendix C. Effect of Nozzle Angle on Dilution................................................................... 32

ii

EXECUTIVE SUMMARY

Additional dilution simulations are presented for the disposal of brine

concentrate resulting from reverse osmosis (RO) seawater desalination into

Monterey Bay, California. The report is a supplement to Roberts (2016) and

addresses new flow scenarios and other issues that have been raised.

It has been suggested to replace the opening in the end gate of the

diffuser with a check valve. A 6-inch valve was proposed, and analyses of

the internal hydraulics of the diffuser and outfall were conducted. The check

valve had minimal effect on the flow distribution between the diffuser ports

and minimal effect on head loss. The flow from the end gate was reduced

slightly and the exit velocity considerably increased. The effect of the valve

orientation on dilution of brine discharges was investigated. It was found

that any upward angle greater than about 20 would result in dilutions that

meet the BMZ salinity requirements. The optimum angle to maximize

dilution is 60.

Dilutions were computed for all new flow scenarios assuming the 6-inch

check valve was installed in the end gate.

The effect of currents on the brine jets was addressed. Dilutions were

predicted using the mathematical model UM3 for the pure brine discharges

for various anticipated current speeds. Jets discharging into the currents

were bent back and dilutions were increased by the current. Jets

discharging with the current were swept downstream and impacted the

seabed farther from the diffuser. All dilutions with currents were greater

than those with zero current, and all impact points were well within the

BMZ.

It has been suggested to orient the nozzles along the diffuser upwards

(from their present horizontal angles) to increase the dilution of dense

effluents. This would decrease the dilution of buoyant effluents, however.

Dilutions were predicted for dense and buoyant effluents. For dense

effluents, increasing the nozzle angle increased dilution considerably; for

buoyant effluents, the dilutions reduced slightly.

iii

LIST OF FIGURES

Figure 1. Seasonally averaged density profiles used for dilution simulations. .................... 3

Figure 2. Characteristics of 6-inch TideFlex check valve Hydraulic Code 355. ................... 8

Figure 3. Typical port flow distributions with and without the endgate check valve for cases T1 and T2. ....................................................................................................... 9

Figure 4. Screen shots of UM3 simulations of dense jet trajectories (Case T2) in counter- and co-flowing currents. Red: zero current; Blue: 10 cm/s; Green: 20 cm/s. ................................................................................................................. 14

Figure 5. Central plane tracer concentrations for dense jets at various nozzle angles

from 15 to 85. After Abessi and Roberts (2015). ............................................... 20

Figure 6. Effect of nozzle angle on normalized dilution of dense jets. After Abessi and Roberts (2015). .......................................................................................................21

Figure 7. Effect of nozzle angle on dilution of dense jets, case T2. .................................... 22

Figure 8. Effect of nozzle angle on dilution for selected buoyant discharge scenarios. .... 23

iv

LIST OF TABLES

Table 1. Seasonally Averaged Properties at Diffuser Depth .................................................. 3

Table 2. Assumed Properties of Effluent Constituents .......................................................... 3

Table 3. Modeled Discharge Scenarios – Project (no GWR) ................................................ 5

Table 4. Modeled Discharge Scenarios – Variant ................................................................. 6

Table 5. Summary of Dilution Simulations for Dense Effluent Scenarios – Project (no GWR) ....................................................................................................................... 11

Table 6. Summary of Dilution Simulations for Dense Effluent Scenarios – Variant ..........12

Table 7. UM3 Simulations of Case T2 with Current ............................................................. 15

Table 8. Effect of Nozzle Angle on Impact Dilution for Flow from End Gate Check Valve for Case T2 (14.08 mgd, 1045.1 kg/m3). .................................................... 16

Table 9. Summary of Dilution Simulations for Buoyant Effluent Scenarios – Project and Variant ............................................................................................................ 18

Table 10. Effect of Nozzle Angle on Dense Jets Case T2. (for conditions, see Table 3) .... 22

Table 11. Effect of nozzle Angle on Dilution for Selected Buoyant Effluent Scenarios ...... 24

Table B1. Additional Modeled Discharge Scenarios ............................................................ 28

Table B2. Summary of Dilution Simulations for Dense Additional Scenarios .................. 29

Table B3. Summary of Dilution Simulations for Buoyant Additional Scenarios .............. 30

Table C1. Further Modeled Discharge Scenarios ................................................................. 32

Table C2. Summary of Dilution Simulations for Dense Scenarios ..................................... 33

Table C3. Summary of Dilution Simulations for Buoyant Further Scenarios .................. 35

1

1. INTRODUCTION

It is proposed to dispose of the brine concentrate resulting from reverse

osmosis (RO) seawater desalination into Monterey Bay, California. Discharge will

be through an existing outfall and diffuser usually used for domestic wastewater

disposal. Because of varying flow scenarios, the effluent and its composition vary

from pure secondary effluent to pure brine. Sixteen scenarios, with flows ranging

from 9.0 to 33.8 mgd (million gallons per day) and densities from 998.8 to 1045.2

kg/m3, were previously analyzed in Roberts (2016). The internal hydraulics of the

outfall and diffuser were computed and dilutions predicted for flow scenarios

resulting in buoyant and dense effluents. It was found that, for all dense discharge

conditions, the salinity requirements in the new California Ocean Plan were met

within the BMZ (Brine Mixing Zone).

Since that report was completed, new flow scenarios have been proposed that

include higher volumes of brine and GWR effluent, the inclusion of hauled brine,

and situations where the desalination plant is offline. It has been requested to

analyze dilutions for many more flow combinations for typical and variant cases.

And it is proposed to replace the opening in the diffuser’s end gate, which allows

some brine to be released at a low velocity and therefore low dilution, with a check

valve that would increase the exit velocity and therefore increase dilution. The

check valve would be angled upwards, further increasing dilution. Finally, it has

been suggested to replace the horizontal 4-inch check valves along the diffuser with

upwardly oriented valves that would increase the dilution of dense effluents.

The specific tasks addressed in this report are:

Analyze internal hydraulics accounting for the effect of the new

proposed end gate check valve;

Compute dilutions for new scenarios with dense and buoyant flow

effluents accounting for the effect of the valve;

Assess the effects of currents on dense discharges;

Compute the dilution of dense discharges from the end gate;

Analyze the effect of varying the nozzle angle on the dilution of dense

and buoyant effluents.

2

2. MODELING SCENARIOS

2.1 Introduction

To address the additional concerns and issues that have been raised, the

revised dilution analyses will include the following:

End-Gate: The outfall hydraulics will be revised assuming the end-

gate has been replaced with one Tideflex valve. The assumed end-gate

configuration may be modified depending on the California Ocean Plan

(COP) compliance analysis results.

Effluent Water Quality: The salinity and temperature of the

secondary effluent and GWR effluent shall remain unchanged from

prior analyses presented in the 2017 Draft EIR/EIS.

Ocean Conditions: Dilution analyses shall incorporate conditions

related to the ocean seasons consistent with previous analyses. Worst-

case conditions shall be assessed and presented.

Mitigation: Preliminary assessments of the impact of diffuser nozzle

orientation on dilution of dense and buoyant effluents will be made.

Currents: The effects of currents on the advection and dispersion of

dense effluents will be assessed.

All revised discharge scenarios will incorporate consideration of a modified

end-gate on outfall diffuser hydraulics and dilution.

Model analyses will be done for typical and high brine discharge scenarios with

a range of secondary and GWR effluent flows. Modeling the highest RO

concentrate flow expected follows the conservative approach previously used on

COP compliance evaluations for this project. Also, scenarios involving high flows

of secondary effluent will be assessed for typical operations of the Variant both

with and without GWR effluent. In addition, it has been requested that discharge

scenarios where brine is absent be included in dilution model analyses to cover

times when the desalination plant is offline.

2.2 Environmental and Discharge Conditions

In the previous report, Roberts (2016), oceanographic measurements obtained

near the diffuser were discussed. Traditionally, three oceanic seasons have been

defined in Monterey Bay: Upwelling (March-September), Oceanic (September-

November), and Davidson (November-March). Density profiles were averaged by

season to obtain representative profiles for the dilution simulations. The profiles

are shown in Figure 1 and are tabulated in Appendix A. The salinities and

temperatures near the depth of the diffuser were averaged seasonally as

summarized in Table 1.

3

Figure 1. Seasonally averaged density profiles used for dilution simulations.

Table 1. Seasonally Averaged Properties at Diffuser Depth

Season Temperature (C)

Salinity (ppt)

Density (kg/m3)

Davidson 14.46 33.34 1024.8 Upwelling 11.48 33.89 1025.8 Oceanic 13.68 33.57 1025.1

The assumed constituent properties are summarized in Table 2.

Table 2. Assumed Properties of Effluent Constituents

Constituent Temperature (C)

Salinity (ppt)

Density (kg/m3)

Secondary effluent 20.0 0.80 998.8 Brine 9.9 58.23 1045.2 GWR 20.0 5.80 1002.6 Hauled brine 20.0 40.00 1028.6

2.3 Discharge Scenarios

Following publication of the 2017 MPWSP Draft EIR/EIS, the MRWPCA

commented on several concerns related to the impact analysis regarding Ocean

Plan and NPDES compliance. Specifically, discharge scenarios involving higher

volumes of desalination brine (following a shut down for repair or routine

4

maintenance) had not been assessed. Also, it was requested that higher resolution

model analysis be conducted for scenarios involving low and moderate flows of

secondary effluent for all project alternatives. Additionally, the MRWPCA

requested that increased GWR effluent flows be assessed as part of planning for an

increased capacity PWM project. Finally, it was requested that hauled brine be

included in the dilution analysis for the Proposed Project.

It is proposed that revised model analysis be completed for typical and high

brine discharge scenarios with secondary effluent flows ranging from 0 to 10 mgd

and with the inclusion of hauled brine. Additionally, scenarios involving high flows

of secondary effluent (15 and 19.78 mgd) will be assessed for typical operations. In

addition, MPWPCA has requested that discharge scenarios where brine is absent

be included in dilution model analyses to cover times when the desal plant is offline

and to revise dilution model estimates based on the modified end-gate which may

alter the outfall diffuser hydraulics.

Table 3 details the revised discharge scenarios for dilution model analysis of

the Proposed Project (full size desalination facility and no implementation of

GWR/PWM).

Table 4 details revised discharge scenarios for dilution model analysis of the

Variant (MPWSP Alternative, reduced capacity desalination facility with

PWM/GWR).

5

Table 3. Modeled Discharge Scenarios – Project (no GWR)

Case ID Scenario Constituent flows (mgd) Combined effluent

Brine Secondary effluent

GWR Hauled brine

Flow (mgd)

Salinity (ppt)

Density (kg/m3)

T1 SE Only 0.00 19.78 0 0.1 19.88 1.00 999.0 T2 Brine only 13.98 0.00 0 0.1 14.08 58.10 1045.1 T3 Brine + Low SE 13.98 1.00 0 0.1 15.08 54.30 1042.0 T4 Brine + Low SE 13.98 2.00 0 0.1 16.08 50.97 1039.4 T5 Brine + Low SE 13.98 3.00 0 0.1 17.08 48.04 1037.0 T6 Brine + Low SE 13.98 4.00 0 0.1 18.08 45.42 1034.9 T7 Brine + Moderate SE 13.98 5.00 0 0.1 19.08 43.08 1033.0 T8 Brine + Moderate SE 13.98 6.00 0 0.1 20.08 40.98 1031.3 T9 Brine + Moderate SE 13.98 7.00 0 0.1 21.08 39.07 1029.7

T10 Brine + Moderate SE 13.98 8.00 0 0.1 22.08 37.34 1028.3 T11 Brine + Moderate SE 13.98 9.00 0 0.1 23.08 35.76 1027.1 T12 Brine + High SE 13.98 10.00 0 0.1 24.08 34.30 1025.9 T13 Brine + High SE 13.98 15.00 0 0.1 29.08 28.54 1021.2 T14 Brine + High SE 13.98 19.78 0 0.1 33.86 24.63 1018.1 T15 High Brine only 16.31 0.00 0 0.1 16.41 58.12 1045.1 T16 High Brine + Low SE 16.31 1.00 0 0.1 17.41 54.83 1042.5 T17 High Brine + Low SE 16.31 2.00 0 0.1 18.41 51.89 1040.1 T18 High Brine + Low SE 16.31 3.00 0 0.1 19.41 49.26 1038.0 T19 High Brine + Low SE 16.31 4.00 0 0.1 20.41 46.89 1036.1 T20 High Brine + Moderate SE 16.31 5.00 0 0.1 21.41 44.73 1034.3

6

Table 4. Modeled Discharge Scenarios – Variant

Case ID Scenario Constituent Flows (mgd) Combined effluent

Brine Secondary effluent

GWR Hauled brine

Flow (mgd)

Salinity (ppt)

Density (kg/m3)

V1 Brine only 8.99 0.00 0 0.0 8.99 58.23 1045.2 V2 Brine + Low SE 8.99 1.00 0 0.0 9.99 52.48 1040.6 V3 Brine + Low SE 8.99 2.00 0 0.0 10.99 47.78 1036.8 V4 Brine + Low SE 8.99 3.00 0 0.0 11.99 43.86 1033.6 V5 Brine + Low SE 8.99 4.00 0 0.0 12.99 40.55 1030.9 V6 Brine + Moderate SE 8.99 5.00 0 0.0 13.99 37.70 1028.6 V7 Brine + Moderate SE 8.99 5.80 0 0.0 14.79 35.71 1027.0 V8 Brine + Moderate SE 8.99 7.00 0 0.0 15.99 33.09 1024.9 V9 Brine + High SE 8.99 14.00 0 0.0 22.99 23.26 1017.0

V10 Brine + High SE 8.99 19.78 0 0.0 28.77 18.75 1013.3 V11 GWR Only 0.00 0.00 1.17 0.0 1.17 5.80 1002.6 V12 Low SE + GWR 0.00 0.40 1.17 0.0 1.57 4.53 1001.6 V13 Low SE + GWR 0.00 3.00 1.17 0.0 4.17 2.20 999.9 V14 High SE + GWR 0.00 23.70 1.17 0.0 24.87 1.04 999.0 V15 High SE + GWR 0.00 24.70 1.17 0.0 25.87 1.03 999.0 V16 Brine + High GWR only 8.99 0.00 1.17 0.0 10.16 52.19 1040.3 V17 Brine + High GWR + Low SE 8.99 1.00 1.17 0.0 11.16 47.59 1036.6 V18 Brine + High GWR + Low SE 8.99 2.00 1.17 0.0 12.16 43.74 1033.5 V19 Brine + High GWR + Low SE 8.99 3.00 1.17 0.0 13.16 40.48 1030.9 V20 Brine + High GWR + Low SE 8.99 4.00 1.17 0.0 14.16 37.67 1028.6 V21 Brine + High GWR + Moderate SE 8.99 5.00 1.17 0.0 15.16 35.24 1026.6 V22 Brine + High GWR + Moderate SE 8.99 5.30 1.17 0.0 15.46 34.57 1026.1 V23 Brine + High GWR + Moderate SE 8.99 6.00 1.17 0.0 16.16 33.11 1024.9 V24 Brine + High GWR + Moderate SE 8.99 7.00 1.17 0.0 17.16 31.23 1023.4 V25 Brine + High GWR + High SE 8.99 11.00 1.17 0.0 21.16 25.48 1018.7 V26 Brine + High GWR + High SE 8.99 15.92 1.17 0.0 26.08 20.82 1015.0 V27 Brine + Low GWR only 8.99 0.00 0.94 0.0 9.93 53.27 1041.2 V28 Brine + Low GWR + Low SE 8.99 1.00 0.94 0.0 10.93 48.47 1037.3 V29 Brine + Low GWR + Low SE 8.99 3.00 0.94 0.0 12.93 41.09 1031.4 V30 Brine + Low GWR + Moderate SE 8.99 5.30 0.94 0.0 15.23 35.01 1026.4 V31 Brine + Low GWR + High SE 8.99 15.92 0.94 0.0 25.85 20.95 1015.1 V32 High Brine only 11.24 0.00 0.00 0.0 11.24 58.23 1045.2 V33 High Brine + Low SE 11.24 0.50 0.00 0.0 11.74 55.78 1043.3 V34 High Brine + Low SE 11.24 1.00 0.00 0.0 12.24 53.54 1041.4 V35 High Brine + Low SE 11.24 2.00 0.00 0.0 13.24 49.55 1038.2 V36 High Brine + Low SE 11.24 3.00 0.00 0.0 14.24 46.13 1035.5 V37 High Brine + Low SE 11.24 4.00 0.00 0.0 15.24 43.16 1033.0 V38 High Brine + Moderate (5) SE 11.24 5.00 0.00 0.0 16.24 40.55 1030.9 V39 High Brine + GWR only 11.24 0.00 1.17 0.0 12.41 53.29 1041.2 V40 High Brine + GWR + Low SE 11.24 0.50 1.17 0.0 12.91 51.25 1039.6 V41 High Brine + GWR + Low SE 11.24 1.00 1.17 0.0 13.41 49.37 1038.0 V42 High Brine + GWR + Low SE 11.24 2.00 1.17 0.0 14.41 46.00 1035.3 V43 High Brine + GWR + Low SE 11.24 3.00 1.17 0.0 15.41 43.07 1033.0 V44 High Brine + GWR + Low SE 11.24 4.00 1.17 0.0 16.41 40.49 1030.9 V45 High Brine + GWR + Moderate SE 11.24 5.00 1.17 0.0 17.41 38.21 1029.0

7

3. OUTFALL HYDRAULICS

3.1 Introduction

The outfall and diffuser is described in Roberts (2016) (see Figure 1 in that

report) as follows:

The Monterey Regional Water Pollution Control Agency (MRWPCA) outfall at

Marina conveys the effluent to the Pacific Ocean to a depth of about 100 ft below

Mean Sea Level (MSL). The ocean segment extends a distance of 9,892 ft from the

Beach Junction Structure (BJS). Beyond this there is a diffuser section 1,406 ft

long. The outfall pipe consists of a 60-inch internal diameter (ID) reinforced

concrete pipe (RCP), and the diffuser consists of 480 ft of 60-inch RCP with a

single taper to 840 ft of 48-inch ID. The diffuser has 171 ports of two-inch

diameter: 65 in the 60-inch section and 106 in the 48-inch section. The ports

discharge horizontally alternately from both sides of the diffuser at a spacing of 16

ft on each side except for one port in the taper section that discharges vertically for

air release. The 42 ports closest to shore are presently closed, so there are 129 open

ports distributed over a length of approximately 1024 ft. The 129 open ports are

fitted with four inch Tideflex “duckbill” check valves (the four inch refers to the

flange size not the valve opening). The valves open as the flow through them

increases so the cross-sectional area is variable. The end gate has an opening at the

bottom about two inches high. The hydraulic characteristics of the four-inch valves

and the procedure to compute the flow distribution in the diffuser with the end

gate opening was detailed in Roberts (2016) Appendix A.

It is proposed to replace the end gate opening with a Tideflex check valve. A

suitable valve is a 6 inch Tideflex check valve, Hydraulic Code 355. The hydraulic

characteristics of this valve are shown in Figure 2.

8

Figure 2. Characteristics of 6-inch TideFlex check valve Hydraulic Code 355.

The same methodology to compute the internal hydraulics as outlined in

Roberts (2016) was used. For the purposes of the hydraulic computations, the

relationship between the total head loss across the valve, E and the flow Q of

Figure 2 was approximated by:

228.24 319.8Q E E (1)

The calculation procedure followed that in Roberts (2o16) except that the open end

gate relationship was replaced by Eq. 1.

Typical flow variations with and without the end gate valve are shown in Figure

3. This shows Case T1, mostly secondary effluent with a total flow of 19.88 mgd,

density 999.0 kg/m3, and case T2, almost pure brine with a flow of 14.08 mgd,

density 1045.1 kg/m3. The flow distributions with and without the Tideflex valve

are virtually indistinguishable. The flow exiting from the end gate is reduced

slightly from 4% to 3% of the total for T1 and from 5% to 4% for T2. The velocity

from the end gate is increased significantly by the check valve, from 6.7 to 10.7 ft/s

for T1 and from 6.1 to 9.7 ft/s for T2. The additional total head loss through the

outfall due to the check valve is negligible, about 0.01 ft.

9

Figure 3. Typical port flow distributions with and without the endgate check valve for cases T1 and T2.

3.2 Effect of End Gate Valve on Dilution

The end gate check valve decreases the flow from the end gate and increases the

flow from the two-inch ports. The dilution calculations later in this report assume

the check valve is in place. To assess the effect of the valve on dilution from the

main diffuser, dilutions were calculated for cases T1 and T2.

For T1, the total flow through the two-inch ports increased from 19.1 to 19.2

mgd (0.5%) and the port diameter increased from 2.00 to 2.01 inches. This had no

effect on dilution (when rounded to a whole number).

For T2, the total flow through the two-inch ports increased from 13.4 to 13.5

mgd (0.8%) and the port diameter was unchanged at 1.84 inches. This had no effect

on dilution (when rounded to a whole number).

10

4. DENSE DISCHARGE DILUTION

4.1 Introduction

The calculation procedure was similar to that in Roberts (2016), where

dilutions were predicted by two methods. First was the semi-empirical equation

due to Cederwall (1968) (Eq. 3 in Roberts, 2016):

5/3

0.54 0.66 0.38i

j j

S z

F dF

(2)

where Si is the impact dilution, Fj the jet densimetric Froude number, and z the

height of the nozzle above the seabed. Second, the dilution and trajectories of the

jets were predicted by UM3, a Lagrangian entrainment model in the mathematical

modeling suite Visual Plumes (Frick et al. 2003, Frick 2004, and Frick and Roberts

2016).

First, the internal hydraulics program was run to determine the flow variation

along the diffuser. Dilutions were then computed for the flow and equivalent nozzle

diameter for the innermost and outermost nozzles and the lowest dilution chosen.

Worst-case oceanic conditions were assumed, which corresponds to the lowest

oceanic density, the “Davidson” condition (Table 1), i.e. salinity = 33.34 ppt,

density = 1024.8 kg/m3.

4.2 Results

The results for the Project scenarios (Table 3) are summarized in Table 5, and

for the Variant (Table 4) in Table 6. For large density differences, the Cederwall

equation gives the lowest dilutions but as the effluent density approaches the

ambient density, UM3 gives lower dilutions. To be conservative, the lowest of the

two model predictions was chosen, as shown in last columns of Tables 5 and 6. The

increase in dilution from the impact point to the edge of the BMZ was assumed to

be 20% as discussed in Roberts (2016).

All dense discharges meet the Ocean Plan requirement of a 2 ppt increment in

salinity at the edge of the BMZ.

11

Table 5. Summary of Dilution Simulations for Dense Effluent Scenarios – Project (no GWR)

Case Effluent conditions Port conditions Predictions

ID Cederwall UM3 At impact (ZID) At BMZ Flow (mgd)

Salinity (ppt)

Density (kg/m3)

Flow (gpm)

Diam. (inch)

Velocity (ft/s)

Froude no.

Dilution Dilution Distance (ft)

Dilution Salinity increment

(ppt)


(ppt

T2 14.08 58.10 1045.1 77.8 1.88 9.0 28.5 15.4 16.2 10.2 15.4 1.61 18.5 1.34 T3 15.08 54.30 1042.0 82.8 1.91 9.3 31.6 16.0 16.1 10.4 16.0 1.31 19.2 1.09 T4 16.08 50.97 1039.4 80.8 1.89 9.2 34.5 16.8 17.6 11.6 16.8 1.05 20.1 0.88 T5 17.08 48.04 1037.0 86.2 1.92 9.6 38.6 17.7 18.5 12.7 17.7 0.83 21.2 0.69 T6 18.08 45.42 1034.9 91.6 1.95 9.8 43.4 18.8 19.5 13.8 18.8 0.64 22.5 0.54 T7 19.08 43.08 1033.0 97.1 1.98 10.1 49.2 20.1 20.9 15.3 20.1 0.48 24.2 0.40 T8 20.08 40.98 1031.3 103.1 2.01 10.4 56.5 21.9 22.2 16.8 21.9 0.35 26.3 0.29 T9 21.08 39.07 1029.7 108.7 2.02 10.9 67.4 24.8 24.9 19.2 24.8 0.23 29.7 0.19 T10 22.08 37.34 1028.3 114.2 2.05 11.1 80.6 28.2 27.5 21.9 27.5 0.15 33.0 0.12 T11 23.08 35.76 1027.1 119.8 2.07 11.4 103.3 34.2 27.7 22.3 27.7 0.09 33.2 0.07 T12 24.08 34.30 1025.9 125.3 2.10 11.6 150.4 46.7 39.2 33.0 39.2 0.02 47.0 0.02 T15 16.41 58.12 1045.1 82.4 1.90 9.3 29.3 15.5 16.3 10.5 15.5 1.60 18.6 1.33 T16 17.41 54.83 1042.5 87.8 1.93 9.6 32.3 16.1 16.9 11.3 16.1 1.34 19.3 1.11 T17 18.41 51.89 1040.1 93.3 1.96 9.9 35.4 16.7 17.5 12.1 16.7 1.11 20.1 0.92 T18 19.41 49.26 1038.0 98.7 1.99 10.2 38.9 17.5 18.4 13.1 17.5 0.91 21.0 0.76 T19 20.41 46.89 1036.1 104.8 2.01 10.6 43.6 18.6 19.3 14.2 18.6 0.73 22.3 0.61 T20 21.41 44.73 1034.3 110.3 2.04 10.8 48.1 19.6 20.4 15.4 19.6 0.58 23.6 0.48

12

Table 6. Summary of Dilution Simulations for Dense Effluent Scenarios – Variant


ID Cederwall UM3 At impact (ZID) At BMZ

Flow (mgd)

Salinity (ppt)

Density (kg/m3)

Flow (gpm)

Diam. (inch)

Velocity (ft/s)

Froude no.



(ppt)


(ppt)

V1 9.0 58.23 1045.2 51.6 1.68 7.5 23.9 15.7 16.0 8.6 15.7 1.59 18.8 1.32

V2 10.0 52.48 1040.6 55.8 1.72 7.7 28.9 16.3 16.9 9.6 16.3 1.17 19.6 0.98

V3 11.0 47.78 1036.8 54.9 1.71 7.7 33.1 17.4 18.1 10.5 17.4 0.83 20.8 0.69

V4 12.0 43.86 1033.6 61.5 1.76 8.1 40.3 18.8 19.8 12.4 18.8 0.56 22.6 0.47

V5 13.0 40.55 1030.9 67.3 1.81 8.4 49.2 20.9 21.6 14.4 20.9 0.35 25.0 0.29

V6 14.0 37.70 1028.6 73.4 1.85 8.8 64.3 24.6 24.9 17.5 24.6 0.18 29.5 0.15

V7 14.8 35.71 1027.0 76.8 1.87 9.0 86.0 30.3 29.4 21.4 29.4 0.08 35.3 0.07

V8 16.0 33.09 1024.9 76.3 1.87 8.9 382.9 110.2 67.6 51.4 67.6 0.00 81.1 0.00

V16 10.2 52.19 1040.3 56.8 1.72 7.8 29.7 16.5 17.3 9.9 16.5 1.14 19.8 0.95

V17 11.2 47.59 1036.6 56.1 1.72 7.8 33.6 17.4 18.3 10.8 17.4 0.82 20.9 0.68

V18 12.2 43.74 1033.5 63.5 1.79 8.1 40.1 18.7 19.3 12.3 18.7 0.56 22.4 0.46

V19 13.2 40.48 1030.9 68.3 1.81 8.5 50.3 21.1 21.8 14.5 21.1 0.34 25.4 0.28

V20 14.2 37.67 1028.6 73.8 1.85 8.8 65.0 24.8 24.9 17.5 24.8 0.17 29.8 0.15

V21 15.2 35.24 1026.6 80.9 1.89 9.3 97.2 33.2 31.7 23.5 31.7 0.06 38.0 0.05

V22 15.5 34.57 1026.1 79.8 1.89 9.1 114.2 37.7 34.3 25.6 34.3 0.04 41.2 0.03

V23 16.2 33.11 1024.9 83.3 1.91 9.3 395.8 113.5 68.5 53.5 68.5 0.00 82.2 0.00

V27 9.9 53.27 1041.2 55.3 1.71 7.7 28.5 16.3 16.9 9.5 16.3 1.22 19.6 1.02

13

Table 6. Summary of Dilution Simulations for Dense Effluent Scenarios – Variant


ID Cederwall UM3 At impact (ZID) At BMZ

Flow (mgd)

Salinity (ppt)

Density (kg/m3)

Flow (gpm)

Diam. (inch)

Velocity (ft/s)

Froude no.



(ppt)


(ppt)

V28 10.9 48.47 1037.3 59.3 1.75 7.9 33.1 17.1 17.8 10.7 17.1 0.88 20.6 0.74

V29 12.9 41.09 1031.4 67.0 1.80 8.5 48.1 20.6 21.1 13.9 20.6 0.38 24.7 0.31

V30 15.2 35.01 1026.4 78.3 1.88 9.1 100.6 34.1 32.6 24.1 32.6 0.05 39.1 0.04

V32 11.2 58.23 1045.2 63.3 1.78 8.2 26.5 15.4 16.1 9.3 15.4 1.61 18.5 1.34

V33 11.7 55.78 1043.3 57.1 1.73 7.8 27.0 15.8 16.5 9.2 15.8 1.42 19.0 1.18

V34 12.2 53.54 1041.4 67.3 1.81 8.4 29.9 16.1 16.8 10.3 16.1 1.26 19.3 1.05

V35 13.2 49.55 1038.2 66.4 1.80 8.4 33.3 16.9 17.8 11.0 16.9 0.96 20.3 0.80

V36 14.2 46.13 1035.5 72.7 1.84 8.8 38.8 18.1 19.0 12.4 18.1 0.71 21.7 0.59

V37 15.2 43.16 1033.0 78.9 1.88 9.1 45.3 19.6 20.3 13.9 19.6 0.50 23.5 0.42

V38 16.2 40.55 1030.9 85.0 1.92 9.4 53.7 21.5 22.0 15.8 21.5 0.33 25.9 0.28

V39 12.4 53.29 1041.2 61.5 1.76 8.1 29.5 16.2 17.0 10.0 16.2 1.23 19.5 1.02

V40 12.9 51.25 1039.6 64.5 1.79 8.2 31.3 16.5 17.3 10.5 16.5 1.09 19.8 0.91

V41 13.4 49.37 1038.0 67.6 1.81 8.4 33.7 17.0 17.8 11.1 17.0 0.95 20.4 0.79

V42 14.4 46.00 1035.3 73.9 1.85 8.8 39.1 18.1 18.8 12.4 18.1 0.70 21.7 0.58

V43 15.4 43.07 1033.0 80.0 1.89 9.2 45.6 19.6 20.2 14.0 19.6 0.50 23.5 0.41

V44 16.4 40.49 1030.9 85.8 1.92 9.5 54.4 21.7 22.3 16.0 21.8 0.33 26.1 0.27

V45 17.4 38.21 1029.0 90.3 1.95 9.7 66.0 24.7 24.7 18.4 24.7 0.20 29.6 0.16

14

4.3 Effect of Currents

The effect of currents on the dynamics of dense jets has been questioned. All

simulations have been done with zero current speed, as this is usually the worst

case that results in lowest dilutions. According to the Research Activity Panel of

the Monterey Bay National Marine Sanctuary, currents in the vicinity of the

diffuser are commonly 5 to 10 cm/s and can reach 20 cm/s.

The effect of currents on dense jets is determined by the dimensionless

parameter urFj (Gungor and Roberts 2009) where ur = ua/u is the ratio of the

ambient current speed, ua, to the jet velocity, u. If 1r ju F the current does not

significantly affect the jet; if 1r ju F the jet will be significantly deflected by the

current and dilution increases significantly. Gungor and Roberts (2009)

investigated the effects of currents on vertical dense jets; experiments on multiport

diffusers with 60 nozzles were reported by Abessi and Roberts (2017).

There are no known experiments on horizontal dense jets in flowing currents

so we investigated the phenomenon using the UM3 model in Visual Plumes. We

simulated the pure brine case, T2 (Table 3) at current speeds of zero, 5, 10, and 20

cm/s. Because of the orientation of the MRWPCA diffuser (see Figure 1 of Roberts

2016) the predominant current direction is expected to be perpendicular to the

diffuser axis. The nozzles are perpendicular to the diffuser, so the current direction

relative to the individual jets is either counter-flow (jets directly opposing the

current), or co-flow (jets in the same direction as the currents.

UM3 was run for all cases. Screen shots of the jet trajectories for counter- and

co-flowing jets are shown in Figure 4.

a) Counter-flow b) Co-flow

Figure 4. Screen shots of UM3 simulations of dense jet trajectories (Case T2) in counter- and co-flowing currents. Red: zero current; Blue: 10 cm/s; Green: 20 cm/s.

15

In counter flowing currents, the jets are bent backwards and impact the seabed

closer to the diffuser. In co-flowing currents, the jets are advected downstream and

impact the seabed farther from the diffuser. The numerical results are summarized

in Table 7.

Table 7. UM3 Simulations of Case T2 with Current

Current Counter-flow Co-flow

Speed (cm/s)

Dilution Impact distance

(ft)


(ft)

0 16.2 10 16.2 10 5 17.3 8 22.6 13

10 18.9 5 38.4 16 20 32.6 0 78.0 27

It can be seen that the effect of the currents is to increase dilution compared to

the zero current case. The maximum impact distance from the diffuser occurs with

co-flowing currents and increases as the current speed increases. In this case, the

maximum impact distance (for ua = 20 cm/s) is 27 ft (8.2 m). Clearly, this is much

less than the distance to the edge of the BMZ (100 m) so we conclude that

neglecting the effect of currents is indeed conservative, and the Ocean Plan

regulations will be met for all anticipated currents.

4.4 Dilution of End Gate Check Valve

As discussed in Section 3, it has been proposed to replace the opening in the

end gate with a 6-inch Tideflex check valve. We simulated the dilution of this valve

for various nozzle angles for the worst case of pure brine, T2 (Table 3). The flow

distributions along the diffuser for this case were shown in Figure 3. The exit

velocity from the end gate check valve is 9.7 ft/s and the equivalent round diameter

is 4.1 inches, yielding a densimetric Froude number, Fj = 20.7.

The effect of nozzle angle on the dilution of dense jets is discussed in Section

6.2. Using Figure 6, the impact dilutions for various angles were calculated. The

results are summarized in Table 8.

The corresponding dilution for the main diffuser nozzles is 15.4 (Table 5). It is

therefore apparent that any nozzle angle greater than about 20 will result in

dilutions greater than the main diffuser and will meet the BMZ requirements.

Dilution is maximized for a 60 nozzle.

16

Table 8. Effect of Nozzle Angle on Impact Dilution for Flow from End

Gate Check Valve for Case T2 (14.08 mgd, 1045.1 kg/m3).

Nozzle angle (Degrees)

Impact dilution

0 8.9 10 12.3 20 18.9 30 25.6 40 31.6 50 35.7 60 36.9

17

5. BUOYANT DISCHARGE DILUTION

5.1 Introduction

The same procedures and models discussed in Roberts (2016) were used

except that all three seasonal profiles were used for each flow scenario to determine

the worst-case condition. Inspection of Tables 3 and 4 show that there are 14 cases

of buoyant discharges, i.e., the effluent density is less than the receiving water

density. Three are for the Project and 11 for the Variant. Two models in the US EPA

modeling suite Visual Plumes were used: NRFIELD and UM3. Zero current speed

was assumed in all cases.

5.2 Results

The following procedure was used: The internal hydraulics program was first

run for each scenario and the average diameter and flow for each nozzle was

obtained. UM3 and NRFIELD were then run for each oceanic season.

As was observed in Roberts (2016), for very buoyant cases, the average dilution

predicted by UM3 is close to the minimum (centerline) dilution predicted by

NRFIELD. They diverge as the effluent becomes only slightly buoyant (i.e. the

effluent density approaches the ambient density), with UM3 dilutions being

considerably higher.

NRFIELD is based on experiments conducted for parameters typical of

domestic wastewater discharges into coastal waters and estuaries. For this

situation, dilution and mixing are mainly dependent on the source buoyancy flux

with momentum flux playing a minor role. As the effluent density approaches the

background density, buoyancy becomes less important and the mixing becomes

dominated by momentum. In that situation, NRFIELD continues to give

predictions but issues a warning that “The results are extrapolated” when the

parameters are outside the range of the original experiments. Table 9 summarizes

the results; NRFIELD predictions are only given when they fall within the

experimental range on which it is based.

The plume behavior depends strongly on the shape of the density profile

(Figure 1) but dilutions are generally very high. The Upwelling profile always gives

deepest submergence and lowest dilutions. The plumes are always submerged with

the Upwelling and Oceanic profiles but some plumes surface with the weak

Davidson stratification. Dilutions are very high for surfacing plumes, up to 842

(Case V12) when the flow is very low.

18

Table 9. Summary of Dilution Simulations for Buoyant Effluent Scenarios – Project and Variant

Case ID Season Effluent conditions Port conditions UM3 simulations NRFIELD simulations Flow

(mgd) Salinity

(ppt) Density (kg/m3)

Flow (gpm)

Diam. (inch)

Velocity (ft/s)

Froude no.

Average dilution

Rise height

(centerline) (ft)

Minimum dilution

Rise height

(centerline) (ft)

Rise height (top) (ft)

T1 Upwelling 19.88 1.00 999.0 103.7 2.01 10.5 27.9 188 57 179 41 57 Davidson 327 100 349 100 100 Oceanic 239 80 238 50 72

T13 Upwelling 29.08 28.54 1021.2 151.6 2.18 13.0 80.6 93 28 Davidson 127 57 Oceanic 94 27

T14 Upwelling 33.86 24.63 1018.1 176.4 2.25 14.2 66.7 99 36 Davidson 147 76 Oceanic 104 41

V9 Upwelling 22.99 23.26 1017.0 119.6 2.10 11.1 50.3 110 37 Davidson 172 75 Oceanic 116 42

V10 Upwelling 28.77 18.75 1013.3 149.9 2.18 12.9 48.3 118 44 100 39 41 Davidson 202 96 215 97 100 Oceanic 132 58 134 57 59



19

Table 9. Summary of Dilution Simulations for Buoyant Effluent Scenarios – Project and Variant

Case ID Season Effluent conditions Port conditions UM3 simulations NRFIELD simulations Flow

(mgd) Salinity


Flow (gpm)

Diam. (inch)

Velocity (ft/s)

Froude no.

Average dilution

Rise height

(centerline) (ft)

Minimum dilution

Rise height

(centerline) (ft)









20

6. DILUTION MITIGATION – EFFECT OF NOZZLE ANGLE

6.1 Introduction

Orienting the nozzles upwards from horizontal will increase the dilution of

brine mixtures that are more dense than the receiving water. For buoyant effluents,

it will decrease dilution slightly. In this section, we investigate the effect on dilution

of varying nozzle orientations for dense and buoyant effluents.

6.2 Dense Effluents

The effect of nozzle angle on dense jets has been recently investigated by Abessi

and Roberts (2015). Figure 5 shows central plane tracer concentrations (inverse of

dilution) obtained by laser-induced fluorescence for dense jets with angles ranging

from 15 to 85. For very shallow angles, e.g. 15, the jet impacts the bed quickly,

reducing dilution. For steep angles, e.g. 85, the trajectory is also truncated and

the jet falls back on itself, which also reduces dilution.

Figure 5. Central plane tracer concentrations for dense jets at various nozzle angles from 15 to 85. After Abessi and Roberts (2015).

21

The optimum angle for dilution is 60. This is illustrated by Figure 6, which

shows the variation with nozzle angle on normalized impact dilution (Si/Fj) and

near field dilution (Sn/Fj) for single jets.

Figure 6. Effect of nozzle angle on normalized dilution of dense jets. After Abessi and Roberts (2015).

Impact dilutions were computed for the “worst-case” of brine only (T2, for

conditions, see Table 3) using Figure 6. The results are tabulated in Table 10 and

plotted in Figure 7. The effect of the height of the nozzle above the seabed, z, is

determined by the dimensionless parameter z/dFj, where d is the nozzle diameter.

For Monterey, the nozzles are four feet above the seabed, so for case T2 we have

z/dFj 0.93. The experiments of Abessi and Roberts were done with nozzles closer

to the bed, with h/dFj ranging from 0.12 to 0.39, so actual dilutions are expected

to be higher than predicted in Table 10.

Dilution calculations with UM3 are also shown for completeness with other

simulations. However, it is known that UM3 considerably underestimates

dilutions for inclined jets (Palomar et al. 2012), therefore only the Abessi and

Roberts results are used.

22

Table 10. Effect of Nozzle Angle on Dense Jets Case T2. (for conditions, see Table 3)

Dilution predictions At impact At BMZ

Case ID

Nozzle angle Cederwall Abessi and

Roberts (2015a) UM3 Dilution Salinity increment Dilution Salinity

increment

(deg) Impact Impact Near field Impact (ppt) (ppt)

T2 0 15.4 - - 16.1 15.4 1.61 18.5 1.34 10 - 16.9 25.2 18.7 16.9 1.47 20.3 1.22 20 - 25.9 37.8 20.9 25.9 0.95 31.1 0.80 30 - 35.3 50.8 22.8 35.3 0.70 42.3 0.59 40 - 43.4 62.3 24.3 43.4 0.57 52.1 0.48 50 - 49.0 70.0 24.5 49.0 0.50 58.9 0.42 60 - 50.7 71.9 24.4 50.7 0.49 60.9 0.41

Figure 7. Effect of nozzle angle on dilution of dense jets, case T2.

Increasing the angle from horizontal (0) to 60 increases dilution

considerably, from 15 to 51. A 30 angle more than doubles the dilution compared

to the horizontal jets.

The dilution at the BMZ is computed as 120% of the impact dilution. Note that

in Table 10 the increase in dilution from the impact point to the end of the near

field is more than 20%. This result, however, is for a single jet, and the increase for

merged jets is less than this, and is conservatively assumed to be 20%, as explained

in Roberts (2016).

23

6.3 Buoyant Effluents

Diffusers for buoyant effluents are usually designed with horizontal nozzles to

maximize the length of the jet trajectory up to the terminal rise height, and

therefore maximize dilution. Inclining the nozzles upwards will usually reduce

dilution, although for very buoyant discharges in deep water the effect may be

minimal. This is because the dynamics are then buoyancy dominated and the effect

of momentum flux and therefore nozzle orientation is unimportant.

For very buoyant discharges, NRFIELD is the preferred model. NRFIELD,

however, assumes the nozzles to be horizontal, so UM3 was used to assess the

effect of nozzle orientation.

Simulations were run with UM3 for selected cases to bracket the expected

results. The chosen cases were for the project scenarios (Table 3): T1 (mainly pure

secondary effluent) and T13 (brine plus high secondary effluent). The latter case is

only slightly buoyant and resulted in the lowest dilution of the buoyant cases. The

simulations were run only for the oceanic conditions that gave the highest dilutions

(Upwelling) and lowest dilutions (Davidson).

The results are summarized in Table 11 and plotted in Figure 8.

Figure 8. Effect of nozzle angle on dilution for selected buoyant discharge scenarios.

The results are insensitive to nozzle angle, especially for the very buoyant case

of mainly pure secondary effluent (T1). Changing the nozzles from horizontal to

60 for the Davidson condition reduces dilution from 327 to 309, and for

Upwelling condition from 188 to 181. For case T13 the corresponding reductions

are from 127 to 105 and from 93 to 75. The percentage reductions for T13 are

greater due to the increased effect of momentum flux, and therefore nozzle angle.

More modest changes in orientation result in lesser effect; for a 30 nozzle the

dilution reductions range from 3 to 13%.

24

Table 11. Effect of nozzle Angle on Dilution for Selected Buoyant Effluent Scenarios

Case ID

Oceanic Season

Effluent conditions Nozzle angle

UM3 simulations

Flow (mgd)

Salinity (ppt)

Density (deg) Average dilution

Rise height

(centerline) (ft)

T1 Upwelling 19.88 1.00 999.0 0 188 57 10 186 58 20 185 58 30 183 59 40 182 60 50 182 61 60 181 61

T1 Davidson 19.88 1.00 999.0 0 327 100 10 323 100 20 319 100 30 311 100 40 313 100 50 311 100 60 309 100

T13 Upwelling 29.08 28.54 1021.2 0 93 28 10 89 29 20 85 30 30 81 31 40 78 33 50 75 35 60 74 37

T13 Davidson 29.08 28.54 1021.2 0 127 57 10 123 57 20 118 57 30 114 58 40 110 60 50 107 61 60 105 63

25

REFERENCES

Abessi, O., and Roberts, P. J. W. (2015). "Effect of nozzle orientation on dense jets in stagnant environments.” J. Hydraul. Eng., 141(8).

Abessi, O., and Roberts, P. J. W. (2017). "Multiport Diffusers for Dense Discharges in Flowing Ambient Water." J. Hydraul. Eng., 143(6).

Frick, W. E., Roberts, P. J. W., Davis, L. R., Keyes, J., Baumgartner, D. J., and George, K. P. (2003). "Dilution Models for Effluent Discharges, 4th Edition (Visual Plumes)." U.S. Environmental Protection Agency, Environmental Research Division, NERL, Standards and Applied Science Division, Office of Science and Technology,

Frick, W. E. (2004). "Visual Plumes mixing zone modeling software." Environmental Modelling & Software, 19, 645-654.

Frick, W. E., and Roberts, P. J. W. (2016). "Visual Plumes 2016: An Updated Public-Domain Plume Model Suite " Proc., International Symposium on Outfall Systems, ISOS2016, IWA. 10 - 13 May 2016.

Gungor, E., and Roberts, P. J. W. (2009). "Experimental Studies on Vertical Dense Jets in a Flowing Current." J. Hydraul. Eng., 135(11), 935-948.

Palomar, P., Lara, J. L., and Losada, I. J. (2012). "Near field brine discharge modeling Part 2: Validation of commercial tools." Desalination, 290(0), 28-42.

Roberts, P. J. W (2016). “Modeling Brine Disposal into Monterey Bay. Final Report” prepared for ESA | Environmental Science Associates, San Francisco, California. July 6, 2016.

26

APPENDIX A. DENSITY PROFILES

The seasonally averaged density profiles assumed for modeling purposes are summarized below.

Depth (m)

Density (kg/m3)

Upwelling Davidson Oceanic

1 1025.1 1024.8 1024.8 3 1025.1 1024.8 1024.8 5 1025.1 1024.8 1024.8 7 1025.2 1024.8 1024.8 9 1025.2 1024.8 1024.8 11 1025.3 1024.8 1024.8 13 1025.4 1024.8 1024.9 15 1025.4 1024.8 1024.9 17 1025.5 1024.8 1024.9 19 1025.6 1024.9 1024.9 21 1025.6 1024.9 1025.0 23 1025.7 1024.9 1025.0 25 1025.7 1024.9 1025.0 27 1025.8 1024.9 1025.1 29 1025.8 1024.9 1025.1 31 1025.8 1024.9 1025.2 33 1025.9 1024.9 1025.2 35 1025.9 1024.9 1025.3

27

APPENDIX B. ADDITIONAL SCENARIOS

In a memorandum from Trussell Technologies, Inc. dated July 21, 2017, dilution simulations for some additional scenarios were requested. They were contained in table 9 of that memo, which is reproduced below.

The flow conditions for these additional scenarios are summarized in Table B1. Dilutions were simulated according to the same procedures as outlined in Sections 4 and 5. The results for dense discharges are summarized in Table B2 and for buoyant discharges in Table B3.

28

Table B1. Additional Modeled Discharge Scenarios

Case ID Scenario Constituent flows (mgd) Combined effluent Brine Secondary

effluent GWR Hauled

brine Flow (mgd)

Salinity (ppt)

Density (kg/m3)

AT1 MPWSP with high 16.31 6.00 0.00 0.0 22.31 42.78 1032.7 AT2 desal brine flow 16.31 7.00 0.00 0.0 23.31 40.98 1031.3 AT3 16.31 8.00 0.00 0.0 24.31 39.33 1030.0 AT4 16.31 9.00 0.00 0.0 25.31 37.81 1028.7 AT5 16.31 10.00 0.00 0.0 26.31 36.40 1027.6 AT6 16.31 12.00 0.00 0.0 28.31 33.89 1025.6 AT7 16.31 14.00 0.00 0.0 30.31 31.70 1023.8 AT8 16.31 16.00 0.00 0.0 32.31 29.79 1022.2 AV9 Variant with desal off 0.00 8.00 1.17 0.0 9.17 1.44 999.3 AV10 Variant with GWR 11.24 6.00 0.00 0.0 17.24 38.24 1029.1 AV11 concentrate off and 11.24 7.00 0.00 0.0 18.24 36.19 1027.4 AV12 high desal brine 11.24 8.00 0.00 0.0 19.24 34.35 1025.9 AV13 flow 11.24 9.00 0.00 0.0 20.24 32.69 1024.6 AV14 11.24 10.00 0.00 0.0 21.24 31.19 1023.4 AV15 11.24 12.00 0.00 0.0 23.24 28.58 1021.3 AV16 11.24 14.00 0.00 0.0 25.24 26.38 1019.5 AV17 11.24 16.00 0.00 0.0 27.24 24.50 1018.0 AV18 Variant with high 11.24 6.00 1.17 0.0 18.41 36.18 1027.4 AV19 desal brine flow 11.24 7.00 1.17 0.0 19.41 34.36 1025.9 AV20 11.24 8.00 1.17 0.0 20.41 32.71 1024.6 AV21 11.24 9.00 1.17 0.0 21.41 31.22 1023.4 AV22 11.24 10.00 1.17 0.0 22.41 29.87 1022.3 AV23 11.24 12.00 1.17 0.0 24.41 27.48 1020.4 AV24 11.24 14.00 1.17 0.0 26.41 25.46 1018.7 AV25 11.24 16.00 1.17 0.0 28.41 23.73 1017.3

29

Table B2. Summary of Dilution Simulations for Dense Additional Scenarios

Case ID Effluent conditions Port conditions Predictions At impact (ZID) At BMZ

Flow (mgd)

Salinity (ppt)

Density (kg/m3)

Flow (gpm)

Diam. (inch)

Velocity (ft/s)

Froude no. Dilution Dilution

Impact distance

(ft) Dilution

Salinity increment

(ppt) Dilution

Salinity increment

(ppt)

AT1 22.3 42.78 1032.7 116.0 2.06 11.2 57.9 22.1 21.4 16.6 21.4 0.42 25.7 0.35 AT2 23.3 40.98 1031.3 120.7 2.08 11.4 60.7 22.8 22.8 18.1 22.8 0.34 27.4 0.28 AT3 24.3 39.33 1030.0 125.5 2.10 11.6 69.2 25.0 24.5 19.8 24.5 0.24 29.4 0.20 AT4 25.3 37.81 1028.7 130.3 2.11 12.0 81.4 28.2 27.2 22.3 27.2 0.16 32.6 0.14 AT5 26.3 36.40 1027.6 135.1 2.13 12.2 97.8 32.5 30.2 25.3 30.2 0.10 36.2 0.08 AT6 28.3 33.89 1025.6 144.7 2.16 12.7 195.3 58.6 44.9 39.0 44.9 0.01 53.9 0.01

AV10 17.2 38.24 1029.1 89.4 1.94 9.7 66.0 24.7 24.6 18.2 24.6 0.20 29.5 0.17 AV11 18.2 36.19 1027.4 93.6 1.96 10.0 86.1 30.0 28.8 22.0 28.8 0.10 34.6 0.08 AV12 19.2 34.35 1025.9 98.4 1.99 10.2 133.0 42.4 37.4 29.7 37.4 0.03 44.9 0.02 AV18 18.4 36.18 1027.4 94.7 1.97 10.0 86.4 30.0 28.7 22.0 28.7 0.10 34.4 0.08 AV19 19.4 34.36 1025.9 99.5 1.99 10.3 135.0 42.9 37.6 29.8 37.6 0.03 45.1 0.02

30

Table B3. Summary of Dilution Simulations for Buoyant Additional Scenarios

Case ID Season Effluent conditions Port conditions UM3 simulations NRFIELD simulations Flow (mgd)

Salinity (ppt)

Density Flow (gpm)

Diam. (inch)

Velocity (ft/s)

Froude no.

Average dilution

Rise height

centerline (ft)

Minimum dilution

Rise height

centerline (ft)

Rise height

top (ft)

AT7 Upwelling 30.31 31.70 1023.8 157.8 2.20 13.3 123.3 88 19 Davidson 120 45 Oceanic 90 17

AT8 Upwelling 32.31 29.79 1022.2 179.2 2.26 14.3 98.6 90 26 Davidson 118 53 Oceanic 88 23

AV9 Upwelling 9.17 1.44 999.3 55.9 1.72 7.7 22.4 244 48 234 35 48 Davidson 467 100 584 67 100 Oceanic 309 66 315 42 60

AV13 Upwelling 20.24 32.69 1024.6 108.9 2.03 10.8 133.6 91 17 Davidson 100 15 Oceanic 138 41





31

Table B3. Summary of Dilution Simulations for Buoyant Additional Scenarios

Case ID Season Effluent conditions Port conditions UM3 simulations NRFIELD simulations Flow (mgd)

Salinity (ppt)

Density Flow (gpm)

Diam. (inch)

Velocity (ft/s)

Froude no.

Average dilution

Rise height

centerline (ft)

Minimum dilution

Rise height

centerline (ft)

Rise height

top (ft)







32

APPENDIX C. EFFECT OF NOZZLE ANGLE ON DILUTION

In order to further investigate the effect of nozzle angle on dilution for various

scenarios, additional model runs were undertaken for horizontal and 60 nozzles. Most were previously analyzed cases, whose flow properties are given in Tables 3 and 4. Table C1 summarizes the properties of the new cases. Dilutions were simulated according to the same procedures as outlined in Sections 4 and 5. Table C2 summarizes the results for dense discharges. For the buoyant cases, only Upwelling and Davidson conditions were run to bracket the expected results. Because NRFIELD only allows for horizontal nozzles, only results for UM3 are shown in Table C3.

Table C1. Further Modeled Discharge Scenarios

Case ID Scenario Constituent flows (mgd) Combined effluent Brine Secondary effluent GWR Hauled brine Flow

(mgd) Salinity


1 GWR only 0.00 0.00 1.17 0.0 1.17 5.80 1002.6 5 0.00 0.40 1.17 0.0 1.57 4.53 1001.6 7 0.00 0.60 1.17 0.0 1.77 4.11 1001.3 12 0.00 2.00 1.17 0.0 3.17 2.65 1000.2 16 0.00 4.00 1.17 0.0 5.17 1.93 999.7 17 0.00 4.50 1.17 0.0 5.67 1.83 999.6 18 0.00 5.00 1.17 0.0 6.17 1.75 999.5 32 0.00 23.40 1.17 0.0 24.57 1.04 999.0

New Variant with normal

flows and GWR offline

8.99 10.00 0.00 0.0 18.99 27.99 1020.8

New2 8.99 6.50 1.17 0.0 16.66 32.14 1024.1 New3 8.99 7.00 1.17 0.0 17.16 31.23 1023.4

33

Table C2. Summary of Dilution Simulations for Dense Scenarios

Effluent conditions Port conditions Impact dilution predictions At impact (ZID) AT BMZ

Case ID

Nozzle angle (deg)

Flow (mgd)

Salinity (ppt)

Density (kg/m3)

Flow (gpm)

Diam. (in.)

Velocity (ft/s)

Froude no.

Cederwall Abessi & Roberts 2015a

UM3 Dilution Salinity incr-

ement (ppt)

Dilution Salinity incr-

ement (ppt)

T5 0 17.08 48.04 1037.0 86.2 1.92 9.6 38.6 17.7 - 18.5 17.7 0.83 21.2 0.69 60 17.08 48.04 1037.0 86.2 1.92 9.6 38.6 - 68.9 - 68.9 0.21 82.6 0.18

T10 0 22.08 37.34 1028.3 114.2 2.05 11.1 80.6 28.2 - 27.5 27.5 0.15 33.0 0.12 60 22.08 37.34 1028.3 114.2 2.05 11.1 80.6 - 143.7 - 143.7 0.03 172.4 0.02

T20 0 21.41 44.73 1034.3 110.3 2.04 10.8 48.1 19.6 - 20.4 19.6 0.58 23.6 0.48 60 21.41 44.73 1034.3 110.3 2.04 10.8 48.1 - 85.7 - 85.7 0.13 102.8 0.11

AT6 0 28.31 33.89 1025.6 144.7 2.16 12.7 194.0 58.3 - 44.9 44.9 0.01 53.9 0.01 60 28.31 33.89 1025.6 144.7 2.16 12.7 194.0 - 345.6 - 345.6 0.00 414.8 0.00

V2 0 9.99 52.48 1040.6 55.8 1.72 7.7 28.9 16.3 - 16.9 16.3 1.17 19.6 0.98 60 9.99 52.48 1040.6 55.8 1.72 7.7 28.9 - 51.5 - 51.5 0.37 61.9 0.31

V4 0 11.99 43.86 1033.6 61.5 1.76 8.1 40.3 18.8 - 19.8 18.8 0.56 22.6 0.47 60 11.99 43.86 1033.6 61.5 1.76 8.1 40.3 - 71.8 - 71.8 0.15 86.1 0.12

V6 0 13.99 37.70 1028.6 73.4 1.85 8.8 64.3 24.6 - 24.9 24.6 0.18 29.5 0.15 60 13.99 37.70 1028.6 73.4 1.85 8.8 64.3 - 114.6 - 114.6 0.04 137.5 0.03

V8 0 15.99 33.09 1024.9 76.3 1.87 8.9 382.9 110.2 - 67.6 67.6 0.00 81.1 0.00 60 15.99 33.09 1024.9 76.3 1.87 8.9 382.9 - 682.3 - 682.3 0.00 818.8 0.00

V16 0 10.16 52.19 1040.3 56.8 1.72 7.8 29.7 16.5 - 17.3 16.5 1.14 19.8 0.95 60 10.16 52.19 1040.3 56.8 1.72 7.8 29.7 - 52.9 - 52.9 0.36 63.5 0.30

V17 0 11.16 47.59 1036.6 56.1 1.72 7.8 33.6 17.4 - 18.3 17.4 0.82 20.9 0.68 60 11.16 47.59 1036.6 56.1 1.72 7.8 33.6 - 59.9 - 59.9 0.24 71.9 0.20

V19 0 13.16 40.48 1030.9 68.3 1.81 8.5 50.3 21.1 - 21.8 21.1 0.34 25.4 0.28 60 13.16 40.48 1030.9 68.3 1.81 8.5 50.3 - 89.6 - 89.6 0.08 107.6 0.07

V22 0 15.46 34.57 1026.1 79.8 1.89 9.1 114.2 37.7 - 34.3 34.3 0.04 41.2 0.03 60 15.46 34.57 1026.1 79.8 1.89 9.1 114.2 - 203.5 - 203.5 0.01 244.2 0.01

V23 0 16.16 33.11 1024.9 83.3 1.91 9.3 395.8 113.5 - 68.5 68.5 0.00 82.2 0.00 60 16.16 33.11 1024.9 83.3 1.91 9.3 395.8 - 705.4 - 705.4 0.00 846.5 0.00

34

Table C2. Summary of Dilution Simulations for Dense Scenarios

Effluent conditions Port conditions Impact dilution predictions At impact (ZID) AT BMZ

Case ID

Nozzle angle (deg)

Flow (mgd)

Salinity (ppt)

Density (kg/m3)

Flow (gpm)

Diam. (in.)

Velocity (ft/s)

Froude no.

Cederwall Abessi & Roberts 2015a

UM3 Dilution Salinity incr-

ement (ppt)

Dilution Salinity incr-

ement (ppt)

V32 0 11.24 58.23 1045.2 63.3 1.78 8.2 26.5 15.4 - 16.1 15.4 1.61 18.5 1.34 60 11.24 58.23 1045.2 63.3 1.78 8.2 26.5 - 47.2 - 47.2 0.53 56.6 0.44

V36 0 14.24 46.13 1035.5 72.7 1.84 8.8 38.8 18.1 - 19.0 18.1 0.71 21.7 0.59 60 14.24 46.13 1035.5 72.7 1.84 8.8 38.8 - 69.1 - 69.1 0.19 82.9 0.15

AV10 0 17.24 38.24 1029.1 89.4 1.94 9.7 65.9 24.7 - 27.5 24.7 0.20 29.6 0.17 60 17.24 38.24 1029.1 89.4 1.94 9.7 65.9 - 117.4 - 117.4 0.04 140.9 0.03

AV12 0 19.24 34.35 1025.9 98.4 1.99 10.2 132.4 42.2 - 37.4 37.4 0.03 44.9 0.02 60 19.24 34.35 1025.9 98.4 1.99 10.2 132.4 - 235.9 - 235.9 0.00 283.1 0.00

V39 0 12.41 53.29 1041.2 61.5 1.76 8.1 29.5 16.2 - 17.0 16.2 1.23 19.5 1.02 60 12.41 53.29 1041.2 61.5 1.76 8.1 29.5 - 52.6 - 52.6 0.38 63.1 0.32

V43 0 15.41 43.07 1033.0 80.0 1.89 9.2 45.6 19.6 - 20.2 19.6 0.50 23.5 0.41 60 15.41 43.07 1033.0 80.0 1.89 9.2 45.6 - 81.2 - 81.2 0.12 97.5 0.10

V45 0 17.41 38.21 1029.0 90.3 1.95 9.7 66.0 24.7 - 18.4 18.4 0.26 22.1 0.22 60 17.41 38.21 1029.0 90.3 1.95 9.7 66.0 - 117.7 - 117.7 0.04 141.2 0.03

AV19 0 19.41 34.36 1025.9 99.5 1.99 10.3 134.4 42.8 - 37.6 37.6 0.03 45.1 0.02 60 19.41 34.36 1025.9 99.5 1.99 10.3 134.4 - 239.4 - 239.4 0.00 287.3 0.00

35

Table C3. Summary of Dilution Simulations for Buoyant Further Scenarios

Effluent conditions Port conditions UM3 simulations

Case ID

Season Flow (mgd)

Salinity (ppt)

Density (kg/m3)

Nozzle angle (deg)

Flow (gpm)

Diam. (inch)

Velocity (ft/s

Froude no.

Average dilution

Rise height

(centerline) (ft)

New Upwelling 18.99 27.99 1020.8 0 98.5 1.99 10.2 62.8 101 28 60 82 34 Davidson 0 145 55 60 123 58

V25 Upwelling 21.16 25.48 1018.7 0 109.8 2.03 10.9 56.2 107 33 60 91 39 Davidson 0 159 65 60 141 70

AV14 Upwelling 21.24 31.19 1023.4 0 114.9 2.06 11.1 96.5 88 20 60 66 28 Davidson 0 124 47 60 94 49

AV21 Upwelling 21.41 31.22 1023.4 0 116.1 2.02 11.6 102.6 91 20 60 68 30 Davidson 0 126 64 60 96 49 1 Upwelling 1.17 5.80 1002.6 0 6.8 0.71 5.5 26.6 499 29 60 488 30 Davidson 0 987 S 60 949 S 5 Upwelling 1.57 4.53 1001.6 0 8.1 0.79 5.3 23.7 461 31 60 447 32 Davidson 0 853 50 60 817 50 7 Upwelling 1.77 4.11 1001.3 0 9.3 0.85 5.3 22.6 443 32 60 428 33 Davidson 0 800 S 60 768 S

36

Table C3. Summary of Dilution Simulations for Buoyant Further Scenarios

Effluent conditions Port conditions UM3 simulations

Case ID

Season Flow (mgd)

Salinity (ppt)

Density (kg/m3)

Nozzle angle (deg)

Flow (gpm)

Diam. (inch)

Velocity (ft/s

Froude no.

Average dilution

Rise height

(centerline) (ft)

12 Upwelling 3.17 2.65 1000.2 0 16.5 1.11 5.5 20.1 359 36 60 347 37 Davidson 0 609 59 60 586 59

16 Upwelling 5.17 1.93 999.7 0 26.9 1.35 6.0 19.9 300 51 60 291 41 Davidson 0 517 S 60 507 S

17 Upwelling 5.67 1.83 999.6 0 29.6 1.40 6.2 19.9 290 S 60 282 S Davidson 0 509 S 60 504 S



New2 Upwelling 16.66 32.14 1024.1 0 86.1 1.92 9.5 103.5 92 18 60 65 26 Davidson 0 131 43 60 95 46

New3 Upwelling 17.16 31.23 1023.4 0 89.0 1.94 9.7 87.0 91 20 60 69 29 Davidson 0 131 46 60 102 48

Modeling Brine Disposal into Monterey Bay

Philip J. W. Roberts, PhD, PE

Consulting Engineer

Atlanta, Georgia, USA

Final report

Prepared for

ESA | Environmental Science Associates

San Francisco, California

July 6, 2016

i

CONTENTS

Contents ..................................................................................................................................... i

Executive Summary .................................................................................................................. i

List of Figures ............................................................................................................................ i

List of Tables ............................................................................................................................ ii

1. Introduction ......................................................................................................................... 1 1.1 Study Purpose .............................................................................................................. 1 1.2 California Ocean Plan ................................................................................................ 2

2. Modeling Scenarios ............................................................................................................ 3 2.1 Environmental Conditions ........................................................................................ 3 2.2 Discharge Scenarios Under Proposed Project .......................................................... 5 2.3 Discharge Scenarios Under Project Variant ..............................................................7 2.4 Updated Model Scenarios .......................................................................................... 9

3. Outfall Hydraulics .............................................................................................................. 12

4. Dense Discharge Dilution .................................................................................................. 14 4.1 Introduction ............................................................................................................... 14 4.2 Results ........................................................................................................................ 16 4.3 Other Considerations ................................................................................................ 19

5. Buoyant Discharge Dilution .............................................................................................. 21 5.1 Introduction ............................................................................................................... 21 5.2 Results ....................................................................................................................... 22

6. Shear and Turbulence Effects .......................................................................................... 24 6.1 Introduction .............................................................................................................. 24 6.2 Plankton Field Data .................................................................................................. 25 6.3 Jet Turbulence and Entrainment ............................................................................ 26 6.4 Results and Discussion ............................................................................................ 30 6.5 Plankton Entrainment and Mortality...................................................................... 33

7. Dilution Mitigation ........................................................................................................... 35 7.1 Introduction .............................................................................................................. 35 7.2 Flow Augmentation .................................................................................................. 36 7.3 Varied Port Flow ....................................................................................................... 39 7.4 Effect of Inclined Nozzles ......................................................................................... 41

7.4.1 Introduction ........................................................................................................ 41 7.4.2 Diffuser Retrofit ................................................................................................. 42 7.4.3 Dedicated Diffuser ............................................................................................. 43 7.4.4 Effect of Inclined Nozzles on Buoyant Flows ................................................... 45

References .............................................................................................................................. 47

Appendix A. Diffuser Hydraulics with Check Valves .......................................................... 49 1. Introduction .............................................................................................................. 49 2. Check Valves ............................................................................................................. 49 3. Port Head Loss .......................................................................................................... 51 4. End Gate Port ........................................................................................................... 52 5. Diffuser and Pipe Head Loss ................................................................................... 52 6. Calculation Procedure .............................................................................................. 53

Appendix B. Density Profiles ................................................................................................. 56

Appendix C. Turbulence Effects on Organisms ....................................................................57 Bibliography ....................................................................................................................... 61

i

EXECUTIVE SUMMARY

It is proposed to dispose of brine concentrate resulting from reverse osmosis

(RO) seawater desalination into Monterey Bay, California. The disposal will be

through an existing outfall and diffuser usually used for domestic wastewater.

Previous analyses of the mixing characteristics and dilution of the effluent are

updated to account for new flow scenarios, new research on the dynamics of dense

jets, the internal hydraulics of the outfall, revision of the California Ocean Plan,

and potential mortality of organisms due to jet-induced turbulence.

The California Ocean Plan (SWRCB, 2015) contains new requirements on

concentrate disposal, in particular the definition of a brine mixing zone (BMZ) at

whose boundary salinity increment limitations must be met and within which

salinity must be estimated. It also requires estimates of the effect of velocity shear

and turbulence on the mortality of larvae and other organisms that are entrained

into the high velocity diffuser jets. New flow scenarios consisting of various

combinations of brine and treated domestic effluent have also been proposed, and

new data on density stratification around the diffuser have been obtained. Finally,

no detailed computations of the internal flow hydraulics of the diffuser have

previously been made to address the variation of flow along the diffuser and its

effect on dilution.

The outfall diffuser consists of “duckbill” check valves whose opening varies

with changing flow rate and it has a fixed opening in the end gate for flushing

purposes. An iterative procedure was used that accounts for the flow

characteristics of the valves, friction losses, and density head. The total head loss

in the outfall and the flow distribution between the various ports were computed

for the various flow scenarios. For dense discharges, the flow per port increases

towards the diffuser end; for buoyant discharges the flows decrease. Flow

variations were generally less than about ±7% from the average flow. About 5% of

the total flow exits from the end gate opening. These flow variations were

accounted for in the dilution simulations.

Several flow and environmental scenarios were analyzed. They consist of

various combinations of brine and brine blended with secondary effluent and GWR

effluent. The flow combinations occur at different times of the year and the

environmental conditions that correspond to each scenario was analyzed. The

most important ambient characteristics that affect dilution are the density

stratification in the water column and the ambient density at the discharge depth.

Density data obtained for the project (Figure 2) were analyzed and seasonal

profiles obtained. The final combinations of flow and ambient conditions that were

analyzed are summarized in Table 6. Zero current speed was assumed for all

dilution calculations.

ii

Dilutions for brine solutions resulting in dense effluents were first computed.

For each flow scenario, the internal hydraulics were computed and the maximum

and minimum flows per port and their corresponding equivalent port diameters

were computed. Dilutions were calculated for each and the lowest dilution

adopted. Dilution was calculated by a semi-empirical equation due to Cederwall

and by the UM3 module of the US EPA model suite Visual Plumes (Table 7). The

results were in close agreement and the Cederwall predictions were adopted as the

most conservative. Minimum (centerline) dilutions on the seabed were generally

greater than 16:1 at distances of about 10 to 30 ft from the diffuser. The salinity

requirement of the Ocean Plan that the salinity increment be less than 2 ppt over

natural background within 100 m from the diffuser was met in all cases. Increases

in salinity are highest on the seabed, and will only be above background for a few

meters above the seabed. They will be zero throughout most of the water column.

Discharges of flows that are positively buoyant were analyzed separately.

Dilution and plume rise height were modeled by the modules UM3 and NRFIELD

of Visual Plumes. NRFIELD is the most appropriate model and its predictions of

minimum dilution were in good agreement with UM3 predictions of average

dilution. The results are summarized in Table 8. Dilutions are generally very high,

always exceeding 100:1, and the plume is usually trapped below the water surface

by the ambient stratification.

For some dense flow cases, particularly when small volumes of secondary

effluent are added to the brine, it is possible that dilutions may not be sufficient to

achieve water quality standards. Mitigation schemes to enhance dilution for these

cases were considered and analyzed, including:

1. Increase the jet velocity and decrease the density difference between the

effluent and receiving water by augmenting the discharges with treated

freshwater from the GWR or desalination facility.

The effect of adding freshwater on dilution for the problematical cases are

shown in Figure 18. Small additions do not substantially increase dilution.

As the effluent density approaches background levels, dilution increases

exponentially. The water quality requirements for these cases could be

achieved by adding about 2 to 4 mgd of freshwater.

2. Vary the flow per port by either temporarily storing on site in a storage

basin and pumping briefly at higher flow rates, by closing off some ports,

or by opening some closed ports.

The effect of varying the flow per port is shown in Figure 20. The dilution

is relatively insensitive to flow rate. As the flow increases, the jet velocity

increases and entrainment increases. However, the check valves also open

offsetting this increase. The flow and heads needed to meet the water

iii

quality requirements are excessive. Varying the flow rate is not an effective

strategy for increasing dilution.

3. Discharge through upwardly inclined nozzles either by retrofitting the

existing horizontal nozzles or by constructing a new dedicated brine

diffuser.

Discharge through upwardly inclined jets increases the length of dense jet

trajectories and increases dilution. Jets at 60 to the horizontal (the de

facto standard) were evaluated. The results are shown in Table 16. The

inclined nozzles increase dilution of dense discharges substantially. All

dilution requirements, including the problematical cases, would be met.

The effect of retrofitting the nozzles on the dilution of positively buoyant

discharges was also evaluated. The effect was small, dilutions were reduced

by less than 10% compared to horizontal nozzles.

The 2015 California Ocean Plan requires an evaluation of “…mortality that

occurs due to shearing stress resulting from the facility’s discharge...” It has been

suggested that planktonic organisms entrained into the high velocity turbulent jets

could be subject to possibly fatal injury. Experimental evidence suggests that the

main effect occurs to organisms whose size is about the same as the small-scale

turbulent eddies, known as the Kolmogorov scales, which subject them to high

strain rates and viscous shear stresses. The effects vary by organism; the relevant

literature is summarized in Appendix C. Surveys of plankton in the vicinity of the

diffuser were made and are summarized in Figure 9. As precise estimates of

plankton mortality due to turbulence are not presently possible several approaches

to this problem are taken.

The turbulence characteristics of jets are reviewed and turbulent length scales

estimated for the various brine discharge scenarios (Table 10). The Kolmogorov

scales range from about 0.012 mm near the nozzle to 2.5 mm at the jet edges at

seabed impact. Exposure of larvae to jet turbulence ranges from a few seconds to

minutes. The scales are smaller than or comparable to the smallest organisms of

interest (Table 9) so some effects may be anticipated. The scales are somewhat

smaller than those due to natural turbulence in the ocean, which is about 1 mm.

Therefore, the Kolmogorov scale of the ocean is also comparable to larvae size and

may cause natural mortality. The major issue is then incremental mortality due to

the jets.

The total volumes in the jets where turbulent intensities are greater than

background effects were computed (Table 10). They are almost infinitesimally

small compared to the volume of the BMZ, ranging from 0.006% to 0.4%.

iv

The fraction of the ambient flow passing over the BMZ that is entrained by the

diffuser, and therefore the fraction of larvae that is entrained, was estimated (Table

10). For the brine discharges, it ranges from 1.7% to 6.4%.

Not all of the organisms that are entrained by the diffuser will die. The fraction

of organisms passing over the diffuser that die is estimated to be less than 0.23%.

As discussed, this is believed to be a very conservative estimate. Total incremental

mortality was also estimated in Table 11.

The volumes entrained into the brine discharges are compared to that for the

present baseline domestic wastewater discharge case (P1). They are much lower,

ranging from 7 to 22%. This is mainly because the dilutions for the domestic

discharges are much higher. Therefore, organism mortality for the brine

discharges would also be expected to be about 7 to 22% of the baseline case.

i

LIST OF FIGURES

Figure 1. MRWPCA outfall near Marina, CA., and sampling locations for water column profiles. Bathymetry is in meters. ............................................................. 3

Figure 2. Seasonal density profiles at the sites shown in Figure 1. ...................................... 4

Figure 3. Seasonally averaged density profiles. ..................................................................... 5

Figure 4. Monthly salinity variations at 27 and 29 m depths. .............................................. 5

Figure 5. The MRWPCA outfall .............................................................................................12

Figure 6. Typical diffuser cross section ................................................................................13

Figure 7. Typical port flow distributions. .............................................................................13

Figure 8. Horizontal dense jet dynamics (DEIR, Appendix D2). ....................................... 14

Figure 9. 3DLIF images of horizontal dense jet (Nemlioglu and Roberts, 2006). ............ 14

Figure 10. Centerline dilution of a horizontal buoyant jet into a stationary homogeneous environment (Roberts et al. 2010). .............................................. 16

Figure 11. Typical graphics output of jet trajectory from UM3: Pure brine case, P2. ........ 17

Figure 12. Cross sections of a jet from a check valve illustrating the transition from elliptical to round shapes. From Lee and Tang (1999). ....................................... 19

Figure 13. Dense jet impacting a local boundary. From Shao and Law (2011). ................ 20

Figure 14. Trapped buoyant plume from multiport diffuser in stratified environment, from Roberts et al. (1989). .....................................................................................21

Figure 15. Graphics outputs from UM3 simulations. .......................................................... 22

Figure 16. Transect lines for plankton samples 5/14/16. ..................................................... 25

Figure 17. LIF image and main properties of a jet ............................................................... 27

Figure 18. Effect on dilution of added freshwater flows to cases V6, V7, and V8. ............. 36

Figure 19. Jet trajectories predicted by UM3 for flow cases V6.10 (red) and V6.14 (blue). ..................................................................................................................... 38

Figure 20. Effect of pumping rate on dilution for flow cases V6, V7, and V8. ................... 39

Figure 21. Jet trajectories predicted by UM3 for flow cases V7.10 (red) and V7.14 (blue). ..................................................................................................................... 41

Figure 22. Laser Induced Fluorescence (LIF) image of a 60 jet and definition diagram. ................................................................................................................. 42

Figure 23. A brine diffuser with multiport rosettes. ............................................................ 43

Figure 24. UM3 predicted trajectories for horizontal (red) and 60 inclined (blue) nozzles for case P1 with upwelling density profile. .............................................. 46

Figure A-1. Typical “Duckbill” Check Valves ....................................................................... 49

Figure A-2. Characteristics of 4” wide bill TideFlex check valve Hydraulic Code 61 ........ 50

Figure A-3. Port and check valve arrangement .................................................................... 51

Figure A-4. End gate opening. .............................................................................................. 52

ii

LIST OF TABLES

Table 1. Seasonal Average Properties at Diffuser Depth........................................................ 5

Table 2. Monthly Average Flows of Secondary Wastewater from the MRWPCS Treatment Plant (mgd) (1998–2012) and Estimated Brine Flows Under the MWPWSP ................................................................................................................. 6

Table 3. Proposed Project Discharge Scenarios ..................................................................... 7

Table 4. Variant Project Discharge Scenarios ........................................................................ 9

Table 5. Assumed Effluent Characteristics ............................................................................. 9

Table 6. Modeled Discharge Scenarios .................................................................................. 11

Table 7. Summary of Dilution Simulations for Dense Effluent Scenarios .......................... 18

Table 8. Summary of Dilution Simulations for Buoyant Effluent Scenarios ...................... 22

Table 9. Summary of Plankton Tows Monterey May 14, 2016 ............................................ 26

Table 10. Summary of Turbulence and Entrainment Calculations ..................................... 32

Table 11. Estimates of entrainment and mortality. Organisms sorted by size, small to large. Case P2 ......................................................................................................... 34

Table 12. Minimum Dms required for Variant Project with GWR concentrate flow (Trussell, 2016) ...................................................................................................... 35

Table 13. Effect of added flow on dilution for selected scenarios........................................ 37

Table 14. Effect of added freshwater volumes ...................................................................... 38

Table 15. Effect of added flow on dilution for selected scenarios ........................................ 40

Table 16. Effect of discharge through 60 nozzles ............................................................... 44

Table 17. Summary of UM3 Dilution Simulations for Buoyant Effluent Scenarios with

Horizontal and 60 Nozzles .................................................................................. 45

1

1. INTRODUCTION

1.1 Study Purpose

It is proposed to dispose of the brine concentrate resulting from reverse

osmosis (RO) seawater desalination into Monterey Bay, California. The disposal

will be through an existing outfall and diffuser usually used for domestic

wastewater disposal. Previous analyses of the mixing characteristics and dilution

of the effluent were made by Flow Science (2008), and updated in 2014 (Flow

Science, 2014) to accommodate new flow scenarios. The 2014 analysis used the

same procedures as the 2008 report although new research on the dynamics of

dense jets has been reported since 2008 and reviews and testimony have raised

new questions. In addition, water quality requirements for concentrate discharges

around the world and the literature on the environmental impacts of brine

discharges were reviewed in SCCWRP (2012), leading to the revision of the

California Ocean Plan (SWRCB, 2016) to include brine discharges. These revisions

include new requirements on concentrate disposal, in particular the definition of a

brine mixing zone (BMZ) at whose boundary salinity increment limitations must

be met and within which salinity must be estimated. New issues were also raised,

particularly the effect of velocity shear and turbulence on the mortality of larvae

and other organisms that are entrained into the high velocity diffuser jets. New

flow scenarios consisting of various combinations of brine and treated domestic

effluent have also been proposed, and new data on density stratification around

the diffuser have been obtained. Finally, no detailed computations of the internal

flow hydraulics of the diffuser have been made to address the variation of flow

along the diffuser and its effect on dilution.

The purpose of this report is to analyze the internal hydraulics of the outfall

and diffuser, to update the analyses of the dynamics and mixing of various

discharge scenarios, and to address the new issues raised, particularly the effects

of velocity shear and jet turbulence.

Specific tasks are:

Compute outfall and diffuser internal hydraulics and flow distribution

accounting for the effects of check valves;

Recompute dilutions for various scenarios of flow and effluent density;

For dense discharges, compute salinity within the BMZ and at its

boundary;

Estimate regions where salinity exceeds 2 ppt;

For buoyant discharges, compute dilutions and plume behavior for the

new oceanic density stratification data;

Address shear and turbulence mortality;

2

Discuss mitigation, i.e. modifications to the diffuser if improvements to

mixing are indicated.

The ambient receiving water conditions and new data are discussed in Section

2.1, and the discharge scenarios are discussed in Sections 2.2 and 2.3 and

summarized in Section 2.4. Details of the outfall and diffuser are presented in

Section 3 and results of the hydraulics analyses are summarized. The calculation

procedure is detailed in Appendix A.

1.2 California Ocean Plan

The 2015 California Ocean Plan (SWRCB, 2016, revised and effective January

28, 2016), contains new requirements to address brine discharges. The most

relevant of these to the present report are contained in Section III.M.3, “Receiving

Water Limitation for Salinity” which states that:

“Discharges shall not exceed a daily maximum of 2.0 parts per thousand

(ppt) above natural background salinity measured no further than 100 meters

(328 ft) horizontally from each discharge point. There is no vertical limit to this

zone…

the Brine Mixing Zone is the area where salinity may exceed 2.0 parts per

thousand above natural background salinity, or the concentration of salinity

approved as part of an alternative receiving water limitation. The standard brine

mixing zone shall not exceed 100 meters (328 feet) laterally from the points of

discharge and throughout the water column…

The brine mixing zone is an allocated impact zone where there may be toxic

effects on marine life due to elevated salinity…

For operational mortality related to discharges, the report shall estimate the

area in which salinity exceeds 2.0 parts per thousand above natural background

salinity or a facility-specific alternative receiving water limitation (see chapter

III.M.3). The area in excess of the receiving water limitation for salinity shall be

determined by modeling and confirmed with monitoring. The report shall use

any acceptable approach approved by the regional water board for evaluating

mortality that occurs due to shearing stress resulting from the facility’s

discharge, including any incremental increase in mortality resulting from a

commingled discharge.”

3

2. MODELING SCENARIOS

2.1 Environmental Conditions

The discharges are to be made through the existing Monterey Regional Water

Pollution Control Agency (MRWPCA) wastewater outfall offshore of Marina,

California, shown in Figure 1. The dynamics and mixing of the discharges depend

on the receiving water density structure and ocean currents. The analyses

presented here assume zero current speed, which is the worst-case condition in

terms of dilution, so the main environmental parameter is the receiving water

density structure. Particularly important is the density difference between the

effluent and receiving water, and, for buoyant discharges, the density stratification

over the water column.

Figure 1. MRWPCA outfall near Marina, CA., and sampling locations for water column profiles. Bathymetry is in meters.

Monthly measurements of CTD (conductivity-temperature-depth) were made

by Applied Marine Sciences (AMS, 2016) over the water column at the four

locations shown in Figure 1. The objective of the monitoring was to gather data

over a two-year period that reflected ocean conditions during this time period

around the MRWPCA outfall. Monthly data were collected between February 2014

and December 2015.

Traditionally, three oceanic seasons have been defined in Monterey Bay:

Upwelling (March-September), Oceanic (September-November), and Davidson

(November-March). Therefore, the profiles were assessed with consideration given

to these seasons, as well as over the entire sampling period.

4

It was found that there was little variation between the profiles taken at the

four sites in any one day, so they were averaged together; they are plotted by season

in Figure 2. The Upwelling season showed the most variable vertical structure in

temperature and density. The Oceanic and Davidson seasons showed weak

stratifications with essentially well-mixed temperature profiles with the oceanic

season somewhat cooler than Davidson. Salinity was fairly uniform over depth so

density was often controlled by temperature. The Upwelling season showed the

strongest stratifications over the water column, and the profiles separate into two

distinct groups with stratification for the other seasons being generally quite weak.

Density differences over the water column ranged from zero (homogeneous) in

December 2012 to 1.17 kg/m3 in August 2014. For most of the profiles the density

differences over the water column ranges from 0.11 to 0.65 kg/m3.

Figure 2. Seasonal density profiles at the sites shown in Figure 1.

The profiles within each season were then averaged to obtain representative

profiles for the dilution simulations. The profiles are shown in Figure 3 and are

tabulated in Appendix B.

Monthly variations of salinity near the depth of the diffuser (assumed to be the

measurements around 27 to 29 m) are shown in Figure 4. The salinities vary

seasonally, but little between the sites or the chosen depths. The bottom salinities

and temperatures were averaged seasonally as summarized in Table 1.

5

Figure 3. Seasonally averaged density profiles.

Figure 4. Monthly salinity variations at 27 and 29 m depths.

Table 1. Seasonal Average Properties at Diffuser Depth

Season Temperature (C)

Salinity (ppt)

Density (kg/m3)

Davidson 14.46 33.34 1024.8 Upwelling 11.48 33.89 1025.8 Oceanic 13.68 33.57 1025.1

2.2 Discharge Scenarios Under Proposed Project

The Monterey Peninsula Water Supply Project (MPWSP) Desalination Plant

would treat the source oceanic water at a 42 percent recovery rate to produce 9.5

6

mgd of desalinated product water. Approximately 14 mgd of brine would be

generated, consisting of concentrates from the pretreatment and reverse osmosis

(RO) processes as well as waste effluent produced during routine backwashing and

operation and maintenance of the pretreatment filters. The brine generated in the

desalination process would be discharged into Monterey Bay through the

MRWPCA’s existing ocean outfall. The outfall consists of an 11,260-foot-long

pipeline terminating in a diffuser with 129 operational ports at a depth of

approximately 100 feet. The outfall and diffuser and their internal hydraulics are

discussed further in Section 3.

During certain times of the year, the brine would be blended with treated

wastewater (when available) from the MRWPCA Regional Wastewater Treatment

Plant, forming a combined discharge. Table 2 (Table 4.3-8 from the DEIR) shows

the monthly projected brine flows from the MPWSP Desalination Plant and the

average monthly wastewater flows from MRWPCA.

Table 2. Monthly Average Flows of Secondary Wastewater from the MRWPCS Treatment Plant (mgd) (1998–2012) and Estimated Brine Flows Under the MWPWSP

Months Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

Brine-Only 13.98 13.98 13.98 13.98 13.98 13.98 13.98 13.98 13.98 13.98 13.98 13.98

Treated Wastewater from MRWPCA 19.78 18.41 14.68 7.02 2.40 1.89 0.90 1.03 2.79 9.89 17.98 19.27

Combined Discharge (Brine+wastewater) 33.76 32.39 28.66 21.00 16.38 15.87 14.88 15.01 16.77 23.87 31.96 33.25

NOTE: Shaded cells represent the seasonal discharge scenarios used in the analysis of operational water quality impacts. Numbers in italics represent the flow rates used in the modeling analysis of salinity (discussed in Impact 4.3-5), the results of which were used to analyze other constituents in the brine and combined discharges (discussed below in this impact analysis). In the case of the combined discharge, the modeling analysis also used low wastewater flow rates of 0.25, 0.5, 1, and 2 mgd and a moderate flow of 9 mgd. SOURCES: MRWPCA, 2013; Trussell Technologies, 2015 in DEIR Appendix D4.

As shown in Table 2, the treated wastewater flow varies throughout the year,

with the highest flows observed during the non-irrigation season (November

through March) and the lowest flows during the irrigation season (April through

October), when the treated wastewater is processed through the SVRP for tertiary

treatment and distributed to irrigators through the Castroville Seawater Intrusion

Project (CSIP).

During the irrigation season, on some days, all of the wastewater flows could

be provided to irrigators, and only the project brine would be discharged into

Monterey Bay through the outfall. The analysis presented in the DEIR assumed

that the brine would be discharged without dilution during the entire irrigation

season (dry months), reflected in scenario 2 in Table 3.

7

During the non-irrigation season (wet months), the analysis presented in the

DEIR assumed that a combined discharge (i.e. brine blended with treated

wastewater) would be released. For the combined discharge scenario, the data

analysis accounted for different wastewater flows ranging from 19.78 mgd in the

winter/Davidson season (when higher discharge flows are anticipated) to lower

flows of 1 and 2 mgd (Table 3). Scenarios 3 through 6 reflect the proposed

combined project discharges during the non-irrigation season as well as during the

irrigation season when a low volume of secondary effluent is discharged.

Table 3. Proposed Project Discharge Scenarios

No. Scenario Discharge flows

(mgd) Secondary

Effluent Desal Brine

1 Baseline 19.78a 0 2 Desal only 0 13.98 3 Desal and low SEb 1 13.98 4 Desal with low SE 2 13.98 5 Desal with moderate SE 9 13.98 6 Desal with high SE 19.78 13.98

a All model scenarios involving high secondary effluent flows used for assessing impacts related to the proposed and variant project conditions use the maximum documented average wet season wastewater flow of 19.78 mgd. b Secondary effluent

2.3 Discharge Scenarios Under Project Variant

Under the Project Variant, the MPWSP Desalination Plant would treat 15.5

mgd of source water at a 42 percent recovery rate. Approximately 8.99 mgd of

brine would be generated, consisting of concentrates from the pretreatment and

reverse osmosis (RO) processes as well as waste effluent produced during routine

backwashing and operation and maintenance of the pretreatment filters. The brine

generated in the desalination process would be discharged through the MRWPCA

ocean outfall as with the Proposed Project (above).

The Project Variant would also include operation of the proposed

Groundwater Replenishment Project (GWR) Project, which would involve RO

treatment of a minimum of 3.9 mgd of source water to produce 3.2 mgd of product

water and 0.73 mgd of effluent1. Operation of the Project Variant would result in

discharge scenarios that would include brine from the MPWSP Desalination Plant,

1 A minimum of 4,320 acre-feet per year (AFY) of source water would be treated to produce 3,500 AFY of product water. At the time of this analysis, the available data for the GWR Project, i.e., 0.73 mgd of GWR effluent flow was used for the modeling analysis (also see Flow Science, Inc., 2014).

8

and/or effluent from the proposed GWR project, and/or treated wastewater from

the existing MRWPCA wastewater treatment plant. Depending on the operational

scenario, the following discharges (also summarized in Table 4) would be released

into Monterey Bay through the MRWPCA outfall:

Variant Scenario 1, Brine-only: 8.99 mgd of brine would be generated at the

Desalination Plant and discharged alone through the MRWPCA outfall. This

operating scenario would occur if the GWR Project comes on line after the MPWSP

Desalination Plant, or the GWR Project periodically shuts down.

Variant Scenarios 2 through 5, Brine-with-Wastewater: 8.99 mgd of brine

would be discharged with varying volumes of treated wastewater from the

MRWPCA Regional Wastewater Treatment Plant. This operating scenario would

occur when treated wastewater is available and if the GWR Project comes on line

after the MPWSP Desalination Plant, or the GWR Project periodically shuts down.

(Previously modeled, no update needed) GWR-only discharge: 0.94 v of

effluent generated under the MRWPCA-proposed GWR Project would be

discharged alone through the MRWPCA outfall. This operating scenario would

occur if the GWR Project comes on line before the MPWSP Desalination Plant, or

the MPWSP Desalination Plant periodically shuts down.

Variant Scenario 6, Blended discharge: 8.99 mgd of brine generated from

the MPWSP Desalination Plant would be blended with 0.94 mgd of GWR-effluent.

This operating scenario would typically occur in the irrigation season.

Variant Scenarios 7 through 10, Combined discharge: The blended

discharge (brine and GWR effluent) would be combined with varying volumes of

treated wastewater from the MRWPCA Regional Wastewater Treatment Plant.

This operating scenario would typically occur in the non-irrigation season.

Not Modeled, GWR-with-Wastewater: 0.94 mgd of GWR-effluent would

be discharged with varying volumes of treated wastewater from the MRWPCA

Regional Wastewater Treatment Plant without brine generated from the MPWSP

Desalination Plant. This operating scenario would occur when treated wastewater

is available and if the GWR Project comes on line before the MPWSP Desalination

Plant, or the MPWSP Desalination Plant periodically shuts down. These scenarios

have been modeled and impacts assessed and documented in the Final EIR for the

Pure Water Monterey GWR Project (MPWPCA, 2015).

9

Table 4. Variant Project Discharge Scenarios

No Scenario Discharge flows (mgd)

Secondary Effluent Desal Brine GWR

1 Desal only 0 8.99 0 2 Desal and low (1) SE 1 8.99 0 3 Desal and low (2) SE 2 8.99 0 4 Desal and moderate SE 5.8 (Davidson) 8.99 0 5 Desal and high SE 19.78 8.99 0 6 Desal and GWR 0 8.99 0.94 7 Desal and GWR and low (1) SE 1 8.99 0.94 8 Desal and GWR and low (2) SE 3 8.99 0.94 9 Desal and moderate SE and GWR 5.3 (Upwelling) 8.99 0.94

10 Desal and high SE and GWR 15.92 8.99 0.94 Notes: a All model scenarios involving high secondary effluent flows used for assessing impacts related to the proposed and variant project conditions use the maximum documented average wet season wastewater flow of 19.78 mgd.

2.4 Updated Model Scenarios

The assumed effluent characteristics for the three seasonal scenarios are


Table 5. Assumed Effluent Characteristics

Season Brine1 Secondary

Effluent1 GWR

Salinity (PPT)

Temp (°C)

Salinity (PPT)

Temp (°C)

Salinity2 (PPT)

Temp1 (°C)

Upwelling 58.23 9.9 0.8 24 5.8 24.4 Davidson 57.40 11.6 0.8 20 5.8 20.2 Oceanic 57.64 11.1 0.9 24 5.8 24.4

1FlowScience (2014), Table C3 and C6 (p.C-7 and C-17), Appendix C. 2Pure Water Monterey Groundwater Replenishment Project Consolidated FEIR (2016): “The discharge of reverse osmosis concentrate would not involve high salinities because the concentrate would be far less saline than ambient ocean water (5,800 mg/L of TDS compared to 33,000 to 34,000 mg/L). The secondary effluent (approximately 1,000 mg/L of TDS) and GWR reverse osmosis concentrate (approximately 5,000 mg/L of TDS) are relatively light and would rise when discharged.” Note: Salinity value of 4 PPT for GWR effluent estimated in Flow Science (2014).

Using the discharge scenarios in Table 3 for the Proposed Project and in Table

4 for the Project Variant, previous model analyses will be updated as follows:

Revise the near-field brine discharge modeling by adjusting the number of

open ports (129 versus 120 used prior), the height of the ports off the ocean floor

(4 feet versus 3.5 feet used prior), and flow scenarios (Table 2 for the Project and

Table 3 for the Variant).

10

Using the revised modeling for each scenario, compute dilution ratios,

calculate the volume of ocean water that exceeds 2 ppt above ambient, plot the

gradient of salinity between the port and the edge of the Zone of Initial Dilution

ZID, calculate the eddy size and velocity of the plume and determine marine losses

due to shear stress, if any. Also calculate the salinity beyond the ZID but within the

regulatory mixing zone (100 m from the port).

Combining the assumed environmental conditions from Table 1, the flows

from Tables 3 and 4, and the assumed effluent conditions from Table 5, we arrive

at 16 possible flow scenarios. Their conditions are summarized in Table 6. The

Proposed Project scenarios are labeled P1 though P6 and the Project Variant

scenarios are Labeled V1 through V10.

11

Table 6. Modeled Discharge Scenarios

Case No. Season

Background Brine Secondary effluent GWR Combined discharge

Temp. (C)

Salinity (ppt)

Density (kg/m3)

Flow (mgd)

Temp. (C)

Salinity (ppt)

Flow (mgd)

Temp. (C)

Salinity (ppt)

Flow (mgd)

Temp. (C)

Salinity (ppt)

Flow (mgd)

Salinity (ppt)

Density (kg/m3)

P1 Baseline - - - - - - 19.78 20.0 0.8 0 20.0 5.8 19.78 0.80 998.8 P2 Upwelling 11.48 33.89 1025.8 13.98 9.9 58.23 0 24.0 0.8 0 24.4 5.8 13.98 58.23 1045.2 P3 Davidson 14.46 33.34 1024.8 13.98 11.6 57.40 1.00 20.0 0.8 0 20.2 5.8 14.98 53.62 1041.2 P4 Davidson 14.46 33.34 1024.8 13.98 11.6 57.40 2.00 20.0 0.8 0 20.2 5.8 15.98 50.32 1038.5 P5 Davidson 14.46 33.34 1024.8 13.98 11.6 57.40 9.00 20.0 0.8 0 20.2 5.8 22.98 35.23 1026.4 P6 Davidson 14.46 33.34 1024.8 13.98 11.6 57.40 19.78 20.0 0.8 0 20.2 5.8 33.76 24.24 1017.6 V1 Upwelling 11.48 33.89 1025.8 8.99 9.9 58.23 0 24.0 0.8 0 24.4 5.8 8.99 58.23 1045.2 V2 Upwelling 11.48 33.89 1025.8 8.99 9.9 58.23 1.00 24.0 0.8 0 24.4 5.8 9.99 52.48 1040.5 V3 Upwelling 11.48 33.89 1025.8 8.99 9.9 58.23 2.00 24.0 0.8 0 24.4 5.8 10.99 47.78 1036.6 V4 Davidson 14.46 33.34 1024.8 8.99 11.6 57.40 5.80 20.0 0.8 0 20.2 5.8 14.79 35.20 1026.4 V5 Upwelling 11.48 33.89 1025.8 8.99 9.9 58.23 19.78 24.0 0.8 0 24.4 5.8 28.77 18.75 1012.7 V6 Upwelling 11.48 33.89 1025.8 8.99 9.9 58.23 0 24.0 0.8 0.94 24.4 5.8 9.93 53.27 1041.1 V7 Davidson 14.46 33.34 1024.8 8.99 11.6 57.40 1.00 20.0 0.8 0.94 20.2 5.8 10.93 47.78 1036.5 V8 Davidson 14.46 33.34 1024.8 8.99 11.6 57.40 3.00 20.0 0.8 0.94 20.2 5.8 12.93 40.52 1030.6 V9 Upwelling 11.48 33.89 1025.8 8.99 9.9 58.23 5.30 24.0 0.8 0.94 24.4 5.8 15.23 35.01 1026.1 V10 Davidson 14.46 33.34 1024.8 8.99 11.6 57.40 15.92 20.0 0.8 0.94 20.2 5.8 25.85 20.67 1014.7

12

3. OUTFALL HYDRAULICS

The Monterey Regional Water Pollution Control Agency (MRWPCA) outfall at

Marina, shown in Figure 5, conveys the effluent to the Pacific Ocean to a depth of

about 100 ft below Mean Sea Level (MSL). The ocean segment extends a distance

of 9,892 ft from the Beach Junction Structure (BJS). Beyond this there is a diffuser

section 1,406 ft long. The outfall pipe consists of a 60-inch internal diameter (ID)

reinforced concrete pipe (RCP), and the diffuser consists of 480 ft of 60-inch RCP

with a single taper to 840 ft of 48-inch ID. The diffuser has 171 ports of two-inch

diameter: 65 in the 60-inch section and 106 in the 48-inch section. The ports

discharge horizontally alternately from both sides of the diffuser at a spacing of 16

ft on each side except for one port in the taper section that discharges vertically for

air release. The 42 ports closest to shore are presently closed, so there are 129 open

ports distributed over a length of approximately 1024 ft. The 129 open ports are

fitted with four inch Tideflex “duckbill” check valves (the four inch refers to the

flange size not the valve opening). The valves open as the flow through them

increases so the cross-sectional area is variable. The end gate has an opening at the

bottom about two inches high. The effect of the valves on the flow distribution in

the diffuser is discussed in Appendix A.

Figure 5. The MRWPCA outfall

The diffuser section sits on rock ballast as shown in Figure 6. The ports are

approximately six inches above the rock ballast and nominally 54 inches above the

sea bed, although this varies. For the dilution calculations, they are assumed to be

4 ft above the bed. The diffuser is laid on a slope of about 0.011 and the depths of

the open ports range from about 98 to 110 ft below MSL.

13

Figure 6. Typical diffuser cross section

The procedure for analyzing the internal hydraulics of the outfall and diffuser

is discussed in Appendix A. Using these procedures, the head losses and the flow

distribution between the ports and the end gate port were computed for the various

flow scenarios of Table 6. Some typical distributions of flow among the ports, for

scenarios P1 (19.78 mgd of secondary effluent), P2 (13.98 mgd of pure brine), and

P6 (33.76 mgd of brine and secondary effluent) are shown in Figure 7.

Figure 7. Typical port flow distributions.

For the pure brine discharge P2 (density greater than seawater) the flow per

port increases in the offshore direction because of the density head. For the

buoyant discharges P1 and P6 (less dense than seawater) the flow decreases in the

offshore direction. The port discharges vary by about ±7% from the average, and

about 5% of the flow exits from the opening in the end gate. These flow variations

are accounted for in the dilution simulations, and the worst cases for dilution are

chosen.

14

4. DENSE DISCHARGE DILUTION

4.1 Introduction

Discharges that are more dense than the receiving seawater result in a sinking

plume that impacts the sea floor at some distance from the nozzle as shown in

Figure 8. The jet, because of its high exit velocity, entrains seawater that mixes with

and dilutes the effluent.

Figure 8. Horizontal dense jet dynamics (DEIR, Appendix D2).

Three-dimensional laser-induced fluorescence (3DLIF) images of a horizontal

negatively buoyant jet similar to those considered here are shown in Figure 9. The

images are obtained by scanning a laser sheet horizontally thought the flow to

which a small amount of fluorescent dye has been added. The fluoresced light is

captured and converted to tracer concentrations and dilution and imaged by

computer graphics techniques as described in Tian and Roberts (2003). The left

image shows the outer surface of the jet in gray scale and the right image shows

the outer surface as semi-transparent with tracer concentrations in false color in a

vertical plane through the jet centerline.

Figure 9. 3DLIF images of horizontal dense jet (Nemlioglu and Roberts, 2006).

15

It can be seen that high tracer concentrations (i.e. salinity) are confined to a

relatively small volume near the nozzle and attenuate rapidly with distance from

the nozzle. The highest salinity on the floor occurs where the jet centerline impacts

it, and it is the dilution and salinity at this point that is computed here.

In the Flow Science (2014) report, they analyze this situation using a semi-

empirical method and also the mathematical model UM3 in the US EPA model

suite Visual Plumes. In the semi-empirical method, the jet trajectory and impact

point are predicted by an analysis due to Kikkert et al. (2007) and dilution was

then predicted by assuming it to occur from jet-induced entrainment. Although the

Kikkert analysis can be applied, it was derived primarily for upwardly-inclined

dense jets rather than horizontal, as occur here, and the dilution analysis neglects

any effects of buoyancy on entrainment. Furthermore, the Flow Science report

considers the centerline dilution predictions of the entrainment model UM3 to be

unreliable due to a study by Palomar at al. (2012a, 2012b) which concluded that

UM3 (and other entrainment models) underestimated impact dilutions by 50-

65%. They therefore used UM3 average dilutions as estimates of centerline

dilutions. The observations of Palomar et al., however, only applied to jets inclined

upwards at 30 to 60 to the horizontal, where mixing is greater due to

gravitational instabilities. For small fractional density differences, the dynamics of

horizontal dense jets are the same as for positively buoyant jets (with a change in

the sign of the density difference). Therefore, a simpler semi-empirical analysis can

be applied, and UM3, which is well-tested and validated for such situations, is also

applicable. The new analysis and application of UM3 are described below.

For the jet situation shown in Figures 8 and 9 it can be shown that the

centerline dilution Sm at any vertical distance z from the nozzle is given by (Roberts

et al. 2010):

m

j j

S zf

F dF

(1)

where Fj is the densimetric Froude number of the jet:

j

j

o

uF

g d

(2)

uj is the jet velocity, o a o og g is the modified acceleration due to gravity,

g is the acceleration due to gravity, a and o are the ambient and effluent densities,

respectively, and d the (round) nozzle diameter. Experimental measurements of

the centerline dilutions plotted according to Eq. 1 are shown in Figure 10.

16

Figure 10. Centerline dilution of a horizontal buoyant jet into a stationary homogeneous environment (Roberts et al. 2010).

A fit to these data for z/dFj > 0.5 has been suggested by Cederwall (1968):

5/3

0.54 0.66 0.38m

j j

S z

F dF

(3)

which is plotted on Figure 10. This equation is used to predict dilutions below.

The dilution and trajectories of the jets can also be predicted by UM3. UM3 is

a Lagrangian entrainment model described in Frick (2003, 2004).

4.2 Results

The following procedure was followed to determine the dilutions for dense

discharges. First the internal hydraulics program (Section 3) was run for each case

summarized in Table 6 to determine the flow distribution between the ports.

Because the flow varies between the ports and because the effective port diameter

varies with flow rate, it is not immediately obvious where along the diffuser the

lowest dilution will occur. Therefore, dilutions were computed for the innermost

and outermost ports. Depending on flow and density, the innermost ports would

sometimes discharge the lowest flow, and sometimes the highest. The conditions

resulting in lowest dilutions were chosen; sometimes this would occur at the

innermost port and sometimes the outermost.

A typical jet trajectory output from UM3 (for the pure brine case, P2) is shown

in Figure 11. For this case, the jet centerline impacts the seabed about 10 ft from

the nozzle and the jet diameter is about 5 ft. Similar simulations were run for all

dense scenarios, and the results, using the Cederwall formula and UM3, are


17

Figure 11. Typical graphics output of jet trajectory from UM3: Pure brine case, P2.

It is remarkable how close the dilution predictions of UM3 and Cederwall are.

Cederwall’s are generally more conservative, so these values are adopted. Jet

impact distances from UM3 are also shown in Table 7. Jet diameters are generally

much less than the port spacing of 16 ft, so no merging is expected before bottom

impaction. The results are comparable to the Flow Science semi-empirical method.

The worst case, as expected, is the pure brine case, P2. For this case, the

minimum centerline dilution is 15.5 and the salinity increment is 1.6 ppt, well

within the BMZ limit of 2 ppt. The distance up to the impact point can be

interpreted as the Zone of Initial Dilution (ZID). In all cases, the salinity limit is

met within the ZID, whose length ranges from about 9 ft for scenario V1 up to 42

ft for scenario V9, where the density difference is much less and the jet trajectory

is much flatter.

The jets will continue to dilute and will ultimately merge beyond the ZID. The

increase in dilution up to the edge of the BMZ is difficult to estimate as there are

no experiments available for these horizontal dense jet flows. Some guidance can

be obtained from experiments on buoyant jets and inclined dense jets, however.

Roberts et al. (1997) estimates a dilution increase of about 60% from the impact

point to the end of the near field for single (non-merging) 60 inclined jets. For

merged jets or plumes the increase in dilution is less; Abessi and Roberts (2014)

reported a dilution increase of about 22% from impact point to the end of the near

field. This is in keeping with the differences in dilution between non-merged and

merged positively buoyant jets impacting water surfaces reported in Tian et al.

(2004). The spacing between the individual jets on each side of the diffuser is 16 ft

therefore it is conservatively assumed that they will merge within the BMZ and the

increase in dilution from the impact point to the BMZ is 20%. This increase is used

to predict the BMZ dilutions in Table 7.

18

Table 7. Summary of Dilution Simulations for Dense Effluent Scenarios

Case No.

Background conditions

Effluent conditions Port conditions

Cederwall formula UM3 Cederwall at BMZ

Dilution

Salinity

Dilution Impact

distance (ft)

Dilution Salinity incre-ment-(ppt)

Salinity (ppt)

Density (kg/m3)

Salinity (ppt)

Density (kg/m3)

Flow (gpm)

Diam. (in)

Height (ft)

Velocity (ft/s)

Froude no. zo/dF

At impact (ppt)

Incre- ment (ppt)

P1 - - 0.80 998.8 - - - - - - - - - - - - -

P2 33.89 1025.8 58.23 1045.2 76.3 1.87 4.0 8.9 29.0 0.89 15.6 35.45 1.56 16.3 10.3 18.7 1.30

P3 33.34 1024.8 53.62 1041.2 75.0 1.86 4.0 8.9 31.4 0.82 16.2 34.60 1.25 16.9 10.7 19.4 1.04

P4 33.34 1024.8 50.32 1038.5 80.8 1.89 4.0 9.2 35.5 0.72 17.0 34.34 1.00 17.8 11.8 20.5 0.83

P5 33.34 1024.8 35.23 1026.4 117.8 2.07 4.0 11.2 120.3 0.19 38.7 33.39 0.05 35.3 29.0 46.5 0.04

P6 33.34 1024.8 24.24 1017.6 188.5 2.28 4.0 14.8 71.5 - - - - - - - -

V1 33.89 1025.8 58.23 1045.2 50.8 1.67 4.0 7.4 25.6 1.12 15.9 35.42 1.53 16.3 8.7 19.0 1.28

V2 33.89 1025.8 52.48 1040.5 54.3 1.70 4.0 7.7 30.1 0.94 16.7 35.00 1.11 17.4 9.8 20.0 0.93

V3 33.89 1025.8 47.78 1036.6 54.6 1.71 4.0 7.6 34.7 0.81 17.7 34.67 0.78 18.5 10.9 21.3 0.65

V4 33.34 1024.8 35.20 1026.4 77.9 1.88 4.0 9.0 102.0 0.25 34.5 33.40 0.05 32.5 24.0 41.4 0.04

V5 33.89 1025.8 18.75 1012.7 160.8 2.21 4.0 13.5 48.9 - - - - - - - -

V6 33.89 1025.8 53.27 1041.1 54.3 1.70 4.0 7.7 29.5 0.96 16.6 35.06 1.17 17.2 9.7 19.9 0.98

V7 33.34 1024.8 47.78 1036.5 58.3 1.74 4.0 7.9 34.2 0.81 17.4 34.17 0.83 18.2 10.9 20.9 0.69

V8 33.34 1024.8 40.52 1030.6 66.5 1.80 4.0 8.4 50.6 0.53 21.3 33.68 0.34 22.1 14.7 25.5 0.28

V9 33.89 1025.8 35.01 1026.1 77.8 1.88 4.0 9.0 260.5 0.10 77.1 33.90 0.01 55.4 42.1 92.5 0.01

V10 33.34 1024.8 20.67 1014.7 143.3 2.16 4.0 12.6 52.6 - - - - - - - -

19

Finally, note that the computed salinities occur only along the seabed.

Salinities decrease with height and will only be above ambient within the spreading

layer on the bottom. For most of the water column, incremental salinities will be

much less than the values in Table 7.

4.3 Other Considerations

The increase in dilution beyond the impact point, or ZID, above is the increase

in dilution up to the end of near field, defined as (Abessi and Roberts, 2014) the

point where the turbulence induced by the discharge collapses under the influence

of its self-induced density stratification. Again, there are no direct experiments to

estimate this distance for this horizontal flow case, but Abessi and Roberts (2014)

estimate the ratio of the near field length to the impact distance to be about 3:1.

The impact distances in Table 7 range from about 9 to 42 ft, so, assuming the ratio

of 3:1 to apply here, the end of the near field will always be within the BMZ distance

of 100 m (328 ft). The assumption that dilution stops at the end of the near field is

a conservative one as further dilution will occur due wave effects and entrainment

as the gravity current flows down the bottom slope.

The dilution calculations assume the discharges to be from round nozzles

whose area is the same as the effective opening of the check valves. There are no

models to predict the dilution from elliptically-shaped check valves but

experiments (Lee and Tang, 1999) show that the centerline dilutions from elliptical

nozzles are greater than from equivalent round nozzles due to the larger surface

area available for entrainment and that the dilutions asymptotically approach

those of equivalent round nozzles at about 12 equivalent jet diameters from the

nozzle.

Figure 12. Cross sections of a jet from a check valve illustrating the transition from elliptical to round shapes. From Lee and

Tang (1999).

Mixing of horizontal dense jets can also be affected by proximity to the local

boundary which may cause a Coanda attachment. Some experiments on this

phenomenon have been reported by Shao and Law (2011); a figure from their paper

is shown in Figure 12. They find that the flow transitions to a wall-dense-jet with

momentum continuing to play a role in mixing. They investigated Coanda

attachment of the jet to the lower boundary and found that none occurred for a

20

parameter which they defined as: 0.12o Mz l . This parameter is essentially the

same as oz dF shown in Table 7. Only case V9 is close to this value and the dilutions

for this cases are very high. It is therefore concluded that Coanda attachment will

not have any effect on the dynamics or mixing of the brine jets. And furthermore,

because of the strong mixing and entrainment in the wall jet region, it is expected

that the additional dilution beyond the impingement point will be actually much

greater than the 20% assumed above.

Figure 13. Dense jet impacting a local boundary. From Shao and Law (2011).

21

5. BUOYANT DISCHARGE DILUTION

5.1 Introduction

Positively buoyant (or just buoyant) discharges, i.e. that have densities less

than the receiving seawater, require different procedures than for negatively

buoyant ones. Inspection of Table 6 shows there are only four positively buoyant

scenarios; P1, the baseline with pure secondary effluent, P6, high volumes of brine

and secondary effluent, and V5 and V10, Project Variants with moderate brine

volumes and high secondary effluent and GWR volumes. Positively buoyant

effluents rise in the water column and are either trapped by the ambient density

stratification if it is strong enough, or reach the water surface if it is weak. A

laboratory photograph of a buoyant discharge from a multiport diffuser into a

stationary stratified environment is shown in Figure 13.

Figure 14. Trapped buoyant plume from multiport diffuser in stratified environment, from Roberts et al. (1989).

The plume dynamics are simulated with two models in Visual Plumes: UM3

and NRFIELD. UM3 is an entrainment model that was previously described.

NRFIELD is based on the experiments on multiport diffusers discharging from two

sides described in Roberts et al. (1989) and subsequently updated with the new

experimental data of Tian et al. (2004) and others. NRFIELD is specifically

designed for conditions typical of very buoyant discharges of domestic effluent

from multiport diffusers into stratified oceanic waters so is judged most

appropriate here. It also includes the lateral spreading after the terminal rise

height and subsequent turbulent collapse at the end of the near field. The primary

outputs from NRFIELD are the minimum (centerline) dilution, the plume rise

height, and wastefield thickness at the end of the near field.

The following procedure was used for the dilution simulations. The internal

hydraulics program, Section 3, was first run for each of the three scenarios. The

average port diameter and flows were then obtained. UM3 and NRFIELD were

then run for the chosen flow and ambient combination scenarios summarized in

Table 6: P1 with Upwelling, Davidson, and Oceanic conditions; P6 with Davidson,

and V5 with Upwelling. The seasonal average density stratifications that were

22

discussed in Section 2.1 and plotted in Figure 3 were used and zero current speed

was assumed. UM3 assumes the discharges are from one side so the usual

assumption was used that the diffuser consists of 129 ports spaced 8 ft apart.

NRFIELD assumes the correct configuration of ports on either side spaced 16 ft

apart; the correction is made internally in Visual Plumes.

5.2 Results

The results are summarized in Table 8 and some graphical jet trajectories from

UM3 are shown in Figure 14. For UM3 the average dilutions at the terminal rise

height are given along with the centerline rise heights, for NRFIELD the near field

(minimum) dilution is given along with the height of the near field (centerline)

dilution and the height to the top of the spreading wastefield layer.

Table 8. Summary of Dilution Simulations for Buoyant Effluent Scenarios

No. Flow rate

(mgd)

Effluent density (kg/m3)

Port diam. (in)

Ocean condition

UM3 simulations NRFIELD simulations

Average dilution

Rise height

(centerline) (ft)

Minimum dilution

Rise height (center

line) (ft)


P1 19.78 998.8 2.00 Upwelling 191 58 186 59 42 P1 19.78 998.8 2.00 Davidson 327 100

(surface) 351 100 100

P1 19.78 998.8 2.00 Oceanic 240 82 239 50 72 P6 33.76 1017.6 2.25 Davidson 154 86 163 86 89 V5 28.77 1012.7 2.18 Upwelling 122 47 105 41 43 V10 25.85 1014.7 2.13 Davidson 195 100

(Surface) 221 100 100

a) P1 Davidson b) P6 Davidson c) V5 Upwelling

Figure 15. Graphics outputs from UM3 simulations.

It can be seen that the average dilution predicted by UM3 is very close to

minimum (centerline) dilution predicted by NRFIELD. Similar observations were

23

made by Isaacson et al. (1983) in connection with physical model studies on the

San Francisco outfall. The reason is apparently that the increase in mixing and

dilution in the transition from vertical to horizontal flow and merging of the

plumes from both sides, neither of which are incorporated into UM3, are

accounted for in the ratio of average to minimum dilutions. Therefore, we use the

average dilution predicted by UM3 but interpret it as the minimum centerline

dilution. Similar observations are reported in model comparisons by Frick and

Roberts (2016). The near field dilution is synonymous with the initial dilution in

the ZID as defined in the California Ocean Plan.

Dilutions are generally high: The lowest is 105 for scenario V5 which was run

with strong (Upwelling) stratification. The highest dilution was 351 for scenario P1

(pure secondary effluent) with weak (Davidson) stratification which resulted in a

surfacing plume. Generally speaking, strong stratification results in lower dilutions

and reduced rise height, and weak stratification result in higher dilutions and

increased rise height. All of the scenarios resulted in submerged plumes except for

case P1 with Davidson conditions.

Note that all the simulations were run for zero current, as specified in the

Ocean Plan. More realistic simulations with currents would predict higher

dilutions and deeper submergences.

The lower density difference and therefore relatively greater influence of

source momentum flux results in flatter jet trajectories, as seen in Figure 14ab,

cases P6 and V5.

24

6. SHEAR AND TURBULENCE EFFECTS

6.1 Introduction

The 2015 California Ocean Plan contains the following requirement for

mitigation of marine life or habitat lost due to a desalination facility:

“For operational mortality related to discharges, the report shall estimate

the area in which salinity exceeds 2.0 parts per thousand above natural

background salinity or a facility-specific alternative receiving water

limitation (see chapter III.M.3). The area in excess of the receiving water

limitation for salinity shall be determined by modeling and confirmed with

monitoring. The report shall use any acceptable approach approved by the

regional water board for evaluating mortality that occurs due to shearing

stress resulting from the facility’s discharge, including any incremental

increase in mortality resulting from a commingled discharge.”

The purpose of this section is to evaluate mortality due to the discharge. In

particular, it has been suggested that planktonic organisms entrained into the high

velocity turbulent jets could be subject to injury, possibly mortality, due to the

effects of turbulence and shear. This is difficult to estimate, so only approximate

orders of magnitude can be made. Somewhat similar concerns arise due to

entrainment into water intakes, for example Tenera (2014), although the

considerations for jets are different and somewhat more complex.

Experimental evidence suggests that the main turbulence effect is caused by

small-scale eddies, known as the Kolmogorov scales, and that most damage may

occur when they are comparable to the size of the organisms. These small eddies

subject the organism to high strain rates and viscous shear stress that may cause

injury or death whereas larger eddies mainly translate the organisms without

causing significant shear. The effects vary by organism, and a number of studies

on the effects of flow and turbulence on marine and freshwater organisms have

been reported. They are summarized in Appendix C.

Most relevant here are the studies of Rehmann et al. (2003) and Jessop

(2007). Rehmann et al. performed laboratory experiments in which zebra mussel

veligers were subject to controlled turbulence in beakers. The turbulence intensity

was such that the Kolmogorov scale, Lk 0.1 mm. They found that mortality

increased sharply to about 65% when the size of the larvae was about 90% of the

Kolmogorov scale. Jessop (2007) measured survival rates in a highly turbulent

tidal channel with 0.06 < Lk < 0.25 mm. Survival rates varied with species; thin-

shelled veligers showed significant mortality of 45% to 64%, but some taxa showed

no mortality.

25

These and other results are difficult to translate to jet turbulence for a number

of reasons. In the laboratory experiments, the organisms were subject to fairly

homogeneous turbulence for long periods: 24 hours. In the field experiment the

turbulence was variable during the organisms’ transit through the channel. The

duration of exposure to high turbulence is unknown but was probably a few

minutes and the variation of conditions during transit are also unknown.

In contrast, the turbulence in jets is not homogeneous: it varies along the

centerline and also laterally across the jet. Kolmogorov scales are smallest near the

nozzle and increase along the trajectory; they are shortest on the centerline and

increase towards the jet edges. Also, transit times of entrained organisms within

the jets are short, of the order of seconds, and vary according to where along the

trajectory they are entrained and how they wander within the jet.

In the following we take several approaches to this problem. In Sections 6.3

and 6.4 we discuss turbulence characteristics of jets and estimate turbulence

length scales for the various brine discharge scenarios. We estimate the total

volumes where effects may be expected and express it as a fraction of the total

volume of the BMZ. Then we estimate the fraction of the ambient flow that passes

over the diffuser that is entrained, and therefore the fraction of larvae entrained.

Finally, in Section 6.5, we estimate the total numbers of organisms entrained by

the diffuser and the number that may be subject to mortality.

6.2 Plankton Field Data

In order to estimate planktonic levels, seawater samples were taken on May

14, 2016 along the three towed transects shown in Figure 16. The results are

summarized by taxonomic group and size ranges in Table 9.

Figure 16. Transect lines for plankton samples 5/14/16.

26

Table 9. Summary of Plankton Tows Monterey May 14, 2016

Taxonomic Group Size (mm) Count (#/m3) Copepods Copepod_unid 0.3 - 5.0 33.73

Calanoid 1.0 - 5.0 3052.72 Oithona_sp 0.5 - 2.0 369.85 Corycaeus_sp 0.3 - 1.5 64.31 Copepod_nauplii 0.1 - 0.2 77.69 Copepod total 3598.29

Other Euphausiid_nauplii 0.35 - 0.5 13.99 Euphausiid_Calyptopis 0.8 - 2.2 613.94 Euphausiid_furcilia 1.0 - 5.6 79.68 Cirripedia_nauplii 0.35 - 0.5 13.83 Pleurobrachia_sp 2.0 - 10.0 3.93 Cladocera_podon 0.2 - 3.0 2.83 Salp 1.0 - 10.0 79.46 Appendicularia_unid 1.0 - 1.5 58.04 Oikopleura_unid 1.0 - 1.5 13.83 Chaetognath_unid 4.0 - 10.0 29.69 Isopod_unid 0.4 - 1.0 1.97 Polychaete_unid 0.5 - 5.0 4.71 Polychaete_trochophore 0.2 - 0.8 2.67 Decapod_zoea 2.0 - 5.0 4.40 Gastropod_larvae 0.8 - 3.0 3.30 Bivalve_veliger 0.75 - 1.0 4.08 Siphonophore 1.0 - 5.0 7.07 Hydromedusa 0.5 - 10 1.41 Other total 938.82 Overall total 4537.11

6.3 Jet Turbulence and Entrainment

The turbulence generated by the diffuser is discussed below, in particular the

spatial variations of turbulence intensity and length scales (eddy sizes) of the

turbulence. The diffuser discharges are initially horizontal and have relatively flat

trajectories (Figures 8, 9, and 11) so it reasonable to analyze them as pure jets (i.e.

flows driven by momentum only).

The properties of jets are well known, and summarized for example in Fischer

et al. (1979). An LIF image of a jet and a depiction of its main features are shown

in Figure 17. Closer to the nozzle the jet is more fine-grained but the turbulent

scales increase along its trajectory. External flow is entrained into the jet (and

dilutes it) and the jet width increases linearly with distance from the nozzle.

27

Figure 17. LIF image and main properties of a jet

Beyond the zone of flow establishment, which is about 6d long, the centerline

velocity um decreases rapidly with distance x according to:

6.2m

du u

x (4)

where u is the jet velocity and d the diameter. The half-width of the jet w, defined

as two standard deviations of a Gaussian velocity distribution, increases linearly

with distance according to:

0.15w x (5)

Combining Eqs. 4 and 5, we see that the average mean shear in the jet du dr where

u is the local velocity and r the radial distance is:

241mudu ud

dr w x (6)

So it decreases even more rapidly than velocity with distance from the nozzle. Note

that the mean shear on the jet centerline is zero.

The turbulence properties in the jet can be estimated from the experimental

data of Webster et al. (2001). They show that the relative turbulence intensity on

the centerline, 0.3mu u where u is the rms value of the turbulent velocity

fluctuations. The intensity decreases with radial distance to zero at the edge of the

jet, defined approximately by Eq. 5.

The size of the small-scale (Kolmogorov) eddies can be estimated from:

28

1/43

(7)

where is the kinematic viscosity of seawater and the energy dissipation rate,

that can be approximated as:

3

L

u

l (8)

where lL is a measure of the largest (energy containing) eddies in the jet. According

to Wygnanski and Fiedler (1969) these length scales also increase linearly with

distance from the nozzle and vary radially across the jet. On the centerline,

0.016Ll x , i.e. about 1/12 of the jet width.

Finally, combining the above equations we find:

3/40.24 Rec

x

(9)

where Re ud is the jet Reynolds number and c the size of the Kolmogorov

eddies on the jet centerline. The Kolmogorov scale therefore increases linearly

along the jet trajectory.

The radial variation of turbulence intensity and turbulent length scales across

the jet is now considered. Near the jet edge, 0.03Ll x according to Wygnanski and

Fiedler, i.e. about 1/25 of the jet width, and the turbulence intensity is about

0.04mu u according to Webster et al. (2001). Combining Eqs. 7 and 8 we can

estimate the ratio of the Kolmogorov scale on the centerline to that at the jet edge

as:

1/4

3 0.2c ec

e c eu u

(10)

where the subscripts c and e refer to the jet centerline and edge, respectively. Eq.

10 indicates that the Kolmogorov scales at the jet edge are about five times larger

than on the centerline.

Travel times of entrained larvae along the jet trajectory will vary, depending

on where along the trajectory they enter the jet and whether they mainly travel on

the centerline, on the edge, or in between. On the centerline, the velocity decreases

according to Eq. 4 so the travel time along the trajectory to the impact point is

given approximately by:

2

0 0 6.2 12.4

L L

m

dx x Lt dx

u ud ud (11)

where L is the length of the trajectory from the nozzle to the seabed impact point.

29

As previously discussed, the jet properties were predicted by UM3 (Table 7).

In addition, the diameters of the jets at impact dj were obtained and the volumes

of the 129 jets computed, assuming them to be conical up to impact:

2

12912

j

j

d LV (12)

This volume was computed as a fraction of the water volume in the BMZ, VBMZ,

computed from:

2

8 310 ft4BMZ

BMZ BMZ

wV L w H H

(13)

where L = 1024 ft is the diffuser length, wBMZ = 656 ft (200 m) is the width of the

brine mixing zone, and H = 104 ft is the average water depth at the diffuser.

In desalination projects, the word entrainment arises in two contexts. It refers

to flow drawn into intakes, and, in the jets and plumes that arise in brine diffusers,

it refers to the flow induced by velocity shear at the edge of the jet (see Figure 17).

This flow, commonly referred to as entrained flow, mixes with and dilutes the

effluent stream. Below we consider the magnitude and spatial variation of the

entrained velocity and the magnitude of the entrained flow expected to be

subjected to significant shear and turbulence effects.

The velocity at which flow is entrained into the jet is directly proportional to

the local centerline velocity and is given by:

o mu u (14)

where uo is the entrainment velocity at a radial distance r = bw from the jet

centerline and bw is defined from the usually assumed radial velocity variation:

2

2expr

m w

u r

u b

(15)

where ur is the entrainment velocity at radial distance r. The length scale bw grows

linearly with x according to (Fischer et al. 1979):

0.107wb x (16)

The variation of the entrained velocity ue with radial distance r beyond the edge of

the jet can be determined by continuity:

2 2o w eu b u r

or we o

bu u

r (17)

30

i.e. the entrained velocity decreases rapidly with distance from the jets in inverse

proportion to the distance r.

Combining Eqs. 4, 13, 15, and 16, we find:

6.2 0.107e

udu

r

Assuming = 0.0535 (Fischer et al., 1979), this becomes:

0.035e

udu

r (18)

In other words, the entrainment velocity is constant with x, the distance along the

jet, but decreases rapidly away from the jet in the radial direction. The

entrainment velocity at any location depends only on the source momentum flux

of the jet, which is proportional to ud.

Now we apply this result to case P2. From Table 7, u = 8.9 ft/s, and d = 1.87

in, yielding:

0.049 ft/seu

r (19)

So, at a distance of 3 ft from the jet centerline, the velocity has fallen to about 0.02

ft/s (0.5 cm/s), already much smaller than typical oceanic velocities.

The total volume entrained into the jets is directly related to dilution. It is given

by (Fischer et al. 1979):

E aQ Q S (20)

where Q is the source discharge rate and Sa the average dilution. The average

dilution Sa = 1.4Sm where Sm is the minimum centerline dilution. So a centerline

dilution of 16:1 requires entraining about 22 times the source flow rate.

The total flux of water passing over the diffuser and BMZ can be estimated

from:

2BMZ BMZQ U L w H (21)

where U is the mean oceanic drift speed. The ADCP measurements of Tenera

(2014) at a depth of 30 m near the mouth of the Monterey Canyon imply a mean

drift speed of about 5 cm/s.

6.4 Results and Discussion

The main flow properties for the various dense discharge scenarios of Tables 6

and 7 were computed according to Eqs. 9 through 21. The results are summarized

in Table 10 where the kinematic viscosity was assumed to be 5 21.2 10 ft /s and

the mean oceanic drift speed 5 cm/sU . In addition, estimates of scales, dilution

31

and entrainment for the baseline domestic wastewater discharge (Case P1, 19.78

mgd) are also shown.

For case P2 (pure brine), the Kolmogorov scale on the centerline ranges from

about 0.012 mm near the nozzle to 0.14 mm at the impact point. At the jet edge it

therefore ranges from about 0.06 mm near the nozzle to about 0.7 mm. The mean

shear rates range from about 57 sec-1 near the nozzle to 0.4 sec-1 at the impact point.

The maximum centerline travel time is about 8 seconds. The mean velocity

profiles of Webster et al. (2001) show that the jet velocity is greater than about 20%

of the maximum over about 80% of the jet width. Therefore, closer to the jet edges,

travel times will be around 40 seconds. Organisms entrained and traveling near

the jet edges will undergo lower intensities (larger eddies) but for longer times.

Clearly, the Kolmogorov scales in the jet will be smaller to or comparable than

the smallest organisms of interest (Table 9). They range from 0.012 to 2.5 mm.

These are mostly somewhat smaller than the Kolmogorov scale due to natural

turbulence in the ocean which in Monterey is about 1 mm (Walter et al. 2014).

Therefore, the Kolmogorov scale of the natural turbulence is also comparable to

larvae size and may cause natural mortality. The incremental mortality due to the

jets are estimated below.

In turbulence, there is a continuous spectrum of eddy sizes and turbulent

kinetic energy from the smallest (Kolmogorov) to the largest (energy-containing)

eddies. For case P2, they range from about 0.01 mm to 0.24 m, so there will be

some eddies of size comparable to the organism sizes that may affect them. It

should be noted, however, that the strain rates (and shear stresses) are maximum

at the Kolmogorov scale and decrease as the eddy size increases.

The volume of water in the jets where turbulent intensities are greater than

background is almost infinitesimally small compared to the volume of the BMZ. It

ranges from 0.006% for case P2 to 0.4% for case V9.

For the brine discharges, only a small fraction of the water passing over the

diffuser is entrained. It ranges from 1.7% for case P2 to 6.4% for case V9. This

estimate depends on the assumed value of the oceanic drift speed, conservatively

assumed to be 5 cm/s. For higher speeds it would be less.

The area of high shear impacted by the diffusers is relatively small and transit

times through this region relatively short. Thus, it seems reasonable to expect that,

while the larvae that experience the highest shear may experience lethal damage,

the overall increase in mortality integrated over the larger area will be low.

The volumes entrained into the brine discharges are much less than into the

baseline (P1) case. This is mainly because the dilutions for the baseline case is

much higher. For the brine discharges the entrainment rates range from 7 to 22%

of those for the baseline case. Therefore, organism mortality for the brine

discharges would also be expected to be about 7 to 22% of the baseline case.

32

Table 10. Summary of Turbulence and Entrainment Calculations

Case No.

Effluent Port conditions UM3 predictions Travel time

centerline

Total volume as % of

BMZ

Kolmogorov scales Entrained flows

Flow Density Velocity Diam. Reynolds number (x10-5)


Diam- eter

Traj- ectory Volume At

1 ft At

impact Volume As % of

BMZ flux

(mgd) (kg/m3) (ft/s) (in) (ft) (in) (ft) (ft3) (sec) (mm) (mm) (mgd)

P1 19.78 998.8 10.0 1.96 1.36 191 - - - - - - 0.01 - 5290 28.5

P2 13.98 1045.2 8.9 1.87 1.16 16.3 10.3 49 12.0 52.4 8.4 0.0064 0.012 0.140 319 1.7

P3 14.98 1041.2 8.9 1.86 1.14 16.9 10.7 51 12.5 59.1 9.1 0.0073 0.012 0.146 354 1.9

P4 15.98 1038.5 9.2 1.89 1.21 17.8 11.8 56 13.6 78.3 10.2 0.0096 0.011 0.153 398 2.1

P5 22.98 1026.4 11.2 2.07 1.62 35.3 29.0 140 31.9 1137.0 42.3 0.1397 0.009 0.290 1136 6.1

P6 33.76 1017.6 14.8 2.28 2.35 - -

V1 8.99 1045.2 7.4 1.67 0.86 16.3 8.7 41 10.4 31.7 8.5 0.0039 0.015 0.152 205 1.1

V2 9.99 1040.5 7.7 1.70 0.91 17.4 9.8 46 11.5 43.6 9.9 0.0054 0.014 0.161 243 1.3

V3 10.99 1036.6 7.6 1.71 0.91 18.5 10.9 50 12.7 58.4 11.9 0.0072 0.014 0.177 285 1.5

V4 14.79 1026.4 9.0 1.88 1.18 32.5 24.0 116 26.5 644.3 40.2 0.0792 0.012 0.305 673 3.6

V5 28.77 1012.7 13.5 2.21 2.07 - -

V6 9.93 1041.1 7.7 1.70 0.91 17.2 9.7 46 11.4 44.0 9.7 0.0054 0.014 0.160 239 1.3

V7 10.93 1036.5 7.9 1.74 0.95 18.2 10.9 52 12.7 61.7 11.3 0.0076 0.014 0.171 278 1.5

V8 12.93 1030.6 8.4 1.80 1.05 22.1 14.7 70 16.6 147.1 17.7 0.0181 0.013 0.208 400 2.2

V9 15.23 1026.1 9.0 1.88 1.17 55.4 42.1 204 46.1 3473.9 121.5 0.4268 0.012 0.531 1181 6.4

V10 25.85 1014.7 12.6 2.16 - -

33

6.5 Plankton Entrainment and Mortality

Estimated rates of organism entrainment into the jets were computed as a

product of the entrained volumes from Table 10 and organism concentrations in

in Table 9. The results are shown in Table 11, sorted by organism size from smallest

to largest. Although the absolute numbers of entrained organisms are high, they

represent only a small fraction of those passing over the diffuser, which is similar

to the fraction of water entrained: about 2 to 6% according to Table 10.

Because the natural Kolmogorov scale near the diffuser is about 1 mm, it is

argued that incremental mortality due to the jets will only occur for regions where

the Kolmogorov scale is shorter than this and by organisms smaller than 1 mm. We

assume no incremental mortality for organisms larger than 1 mm. Organisms

smaller than 1 mm comprise only 27% of the total, and the fraction of them that

actually die is uncertain. According to the literature it could be anywhere from zero

to about 50%; we assume the conservative upper limit of 50%. The results are


We emphasize that 50% is most probably a very conservative upper limit to the

fractional mortality. As discussed, organisms in a jet are subject to its turbulence

for only brief periods of seconds and the turbulence intensity decreases rapidly as

they travel through the jet.

It is useful to combine these estimates to obtain an upper bound for the

fraction of entrained organisms passing over the diffuser that may be subject to

mortality. For case P2, we have, from Tables 10 and 11.

Fraction of Fraction ofFraction

BMZ flux × organisms × 0.017 0.266 0.50 0.0023 0.23%mortality

entrained < 1 mm

Note that similar calculations are made for intakes. For example, Tenera

(2014) estimated larvae entrainment into a proposed intake near the head of the

Monterey Canyon. Because intakes are essentially point sinks, the concept of water

flux passing over them is meaningless so the methods used here do not apply. They

use the ETM (Empirical Transport Model) approach whereby the proportional

mortality of larvae in the source water population is estimated. They estimate the

highest estimated proportional mortality to be of order 0.1% for a 63 mgd intake.

For the diffuser, the volumes entrained for dilution are about 5 to 20 times this

amount so if the same approach were used here approximately 0.5 to 2.0% of the

source flow would be subject to mortality, similar to that estimated in Table 10.

The difference of course is that 100% mortality of entrained organisms is assumed

for intakes whereas a much smaller fraction, if any, larvae die in passing through

the jets.

34

Table 11. Estimates of entrainment and mortality. Organisms sorted by size, small to large. Case P2

Taxonomic Group Size (mm)

Count (#/m3)

% of total

Cumulative %

Entrainment (#/day)

Incremental mortality (#/day)

Copepods Copepod_nauplii 0.1 - 0.2 77.69 1.71 1.71 114,680,910 57,340,455 Other Cladocera_podon 0.2 - 3.0 2.83 0.06 1.77 4,172,099 2,086,050 Other Polychaete_trochophore 0.2 - 0.8 2.67 0.06 1.83 3,940,942 1,970,471 Copepods Copepod_unid 0.3 - 5.0 33.73 0.74 2.58 49,790,726 24,895,363 Copepods Corycaeus_sp 0.3 - 1.5 64.31 1.42 3.99 94,933,608 47,466,804 Other Euphausiid_nauplii 0.35 - 0.5 13.99 0.31 4.30 20,649,175 10,324,588 Other Cirripedia_nauplii 0.35 - 0.5 13.83 0.30 4.61 20,409,510 10,204,755 Other Isopod_unid 0.4 - 1.0 1.97 0.04 4.65 2,902,172 1,451,086 Copepods Oithona_sp 0.5 - 2.0 369.85 8.15 12.80 545,978,077 272,989,039 Other Polychaete_unid 0.5 - 5.0 4.71 0.10 12.91 6,953,004 3,476,502 Other Hydromedusa 0.5 - 10 1.41 0.03 12.94 2,086,050 1,043,025 Other Bivalve_veliger 0.75 - 1.0 4.08 0.09 13.03 6,026,992 3,013,496 Other Euphausiid_Calyptopis 0.8 - 2.2 613.94 13.53 26.56 906,316,100 453,158,050 Other Gastropod_larvae 0.8 - 3.0 3.30 0.07 26.63 4,868,389 2,434,194 Copepods Calanoid 1.0 - 5.0 3052.72 67.28 93.91 4,506,487,870 0 Other Euphausiid_furcilia 1.0 - 5.6 79.68 1.76 95.67 117,622,706 0 Other Salp 1.0 - 10 79.46 1.75 97.42 117,305,750 0 Other Appendicularia_unid 1.0 - 1.5 58.04 1.28 98.70 85,679,028 0 Other Oikopleura_unid 1.0 - 1.5 13.83 0.30 99.01 20,418,019 0 Other Siphonophore 1.0 - 5.0 7.07 0.16 99.16 10,430,248 0 Other Pleurobrachia_sp 2.0 - 10 3.93 0.09 99.25 5,804,344 0 Other Decapod_zoea 2.0 - 5.0 4.40 0.10 99.35 6,492,125 0 Other Chaetognath_unid 4.0 - 10 29.69 0.65 100.00 43,832,517 0

Totals 4537.11 6,697,780,360 891,853,877

35

7. DILUTION MITIGATION

7.1 Introduction

This section explores methods to increase dilution for dense discharges (brine,

and brine comingled with secondary and GWR effluents). In particular, it has been

suggested that some combinations of effluents may not achieve sufficient dilution

to meet the water quality requirements of the Ocean Plan. Particularly troublesome

may be ammonia levels when low to moderate volumes of secondary effluent are

added to brine. Trussell (2016) identifies some cases, reproduced in Table 12,

where the dilutions predicted from Tables 7 and 8 are insufficient to achieve the

target goals of 80% of the compliance limit. Note that the dilution Dm used in Table

9 is 1m mD S where Sm is the dilution in Tables 7 and 8 to agree with the

definition of dilution used in the Ocean Plan. It can be seen that cases V6, V7, and

V8 may not achieve sufficient dilution.

Table 12. Minimum Dms required for Variant Project with GWR concentrate flow (Trussell, 2016)

Case No.

Minimum required Dm for compliance Modeled Dm

WW flow

(mgd)

50% of Dm

required

80% of Dm

required

100% of Dm

required Cederwall UM3 NRFIELD

V6 0.0 69 37 30 15.6 16.2 - V7 1.0 65 41 32 16.4 17.2 - V8 3.0 73 46 37 21.6 22.2 - V9 5.3 80 50 40 76.6 55.0 - V10 15.9 96 60 48 - 194 220

Several possible mitigation strategies have been suggested to increase dilution:

1. Augment the discharges by adding treated RO water to the brine from the

GWR or desalination facility. This would increase the jet velocities and

decrease the density difference between the effluent and receiving water,

both of which will increase dilution.

2. Increase the flow per port by either temporarily storing on site in a storage

basin and pumping briefly at higher flow rates, or by closing off some ports.

Both would increase the jet velocity and increase dilution.

3. Discharge through upwardly inclined nozzles either by retrofitting the

existing horizontal nozzles or by constructing a new dedicated brine

diffuser.

These options are analyzed in this section, focusing on cases V6, V7, and V8.

In addition, the effect of retrofitting upward nozzles on the MRWPCA diffuser on

36

the dilution of positively buoyant discharges is discussed along with some

engineering issues.

7.2 Flow Augmentation

In this scenario, flows with densities close to freshwater are added to the brine

and secondary effluent mixtures to increase jet velocity and decrease the density

difference between the combined effluent and the receiving water.

The following procedure was followed to analyze this scenario. A quantity of

water was added to the base flow and the new flow rate and effluent density were

computed. The internal hydraulics program was then run and the variations in

effective port diameter and flow per port along the diffuser were obtained. The

calculations account for the variation of port opening with flow as explained in

Appendix A. Dilution calculations were then performed for the ports with highest

and lowest flows and the lowest value of dilution chosen. The dilution calculations

were performed using the Cederwall equation (Eq. 3), and UM3 was also run for

some cases to determine jet trajectories.

The results are plotted as functions of flow added in Figure 18 and are

summarized in Table 13. The effect of added flow on the jet trajectories predicted

by UM3 is shown in Figure 19 for two typical cases: V6.10 and V6.14.

Figure 18. Effect on dilution of added freshwater flows to cases V6, V7, and V8.

37

Table 13. Effect of added flow on dilution for selected scenarios

Case No.

Background density

Makeup Flow

Combined flow Port conditions Dilution by Cederwall formula

Flow Density Flow Diam. Height Velocity Froude no. y/dF

(kg/m3) (mgd) (mgd) (kg/m3) (gpm) (cfs) (in) (ft) (ft/s) V6.10 1025.8 0.0 9.9 1041.1 54.3 0.121 1.70 4.0 7.7 29.5 0.96 16.6 V6.11 1025.8 0.5 10.4 1039.0 56.3 0.126 1.72 4.0 7.8 32.0 0.87 17.0 V6.12 1025.8 1.0 10.9 1037.2 58.8 0.131 1.74 4.0 7.9 34.9 0.79 17.6 V6.13 1025.8 2.0 11.9 1033.9 58.6 0.131 1.74 4.0 7.9 41.3 0.67 19.2 V6.14 1025.8 3.0 12.9 1031.1 63.9 0.142 1.78 4.0 8.2 52.6 0.51 21.9 V6.15 1025.8 4.0 13.9 1028.7 72.4 0.161 1.84 4.0 8.7 74.3 0.35 27.3 V6.16 1025.8 5.0 14.9 1026.7 76.3 0.170 1.87 4.0 8.9 136.2 0.19 43.7 V6.17 1025.8 5.3 15.2 1026.1 77.8 0.173 1.88 4.0 9.0 243.6 0.10 72.6 V7.10 1024.8 0.0 10.9 1036.5 58.3 0.130 1.74 4.0 7.9 34.2 0.81 17.4 V7.11 1024.8 0.5 11.4 1034.8 57.2 0.128 1.73 4.0 7.8 36.7 0.76 18.1 V7.12 1024.8 1.0 11.9 1033.2 60.2 0.134 1.75 4.0 8.0 41.0 0.67 19.1 V7.13 1024.8 2.0 12.9 1030.5 66.5 0.148 1.80 4.0 8.4 51.2 0.52 21.4 V7.14 1024.8 3.0 13.9 1028.2 67.3 0.150 1.81 4.0 8.4 66.3 0.40 25.3 V7.15 1024.8 4.2 15.1 1025.8 77.3 0.172 1.87 4.0 9.0 129.8 0.20 42.0 V7.16 1024.8 4.6 15.5 1025.1 78.8 0.176 1.88 4.0 9.1 241.4 0.11 72.0 V7.17 1024.8 4.75 15.7 1024.8 78.8 0.176 1.88 4.0 9.1 1283.9 0.02 353.5 V8.10 1024.8 0.0 12.9 1030.6 66.5 0.148 1.80 4.0 8.4 50.6 0.53 21.3 V8.11 1024.8 0.5 13.4 1029.4 69.3 0.155 1.82 4.0 8.6 57.8 0.46 23.0 V8.12 1024.8 1.0 13.9 1028.3 72.6 0.162 1.84 4.0 8.8 67.5 0.39 25.5 V8.13 1024.8 2.0 14.9 1026.3 76.3 0.170 1.87 4.0 8.9 104.1 0.25 35.1 V8.14 1024.8 2.5 15.4 1025.3 78.3 0.175 1.88 4.0 9.1 182.6 0.14 56.1 V8.15 1024.8 2.8 15.7 1024.8 78.3 0.175 1.88 4.0 9.1 1291.0 0.02 355.4

38

Figure 19. Jet trajectories predicted by UM3 for flow cases V6.10 (red) and V6.14 (blue).

The higher jet velocity and smaller density differences leads to a flatter and

longer trajectory and therefore higher dilution. Of these, the main effect is due to

the decreased density difference because the ports open as the flow increases,

offsetting the increased jet velocity that would occur for a fixed office.

For low added volumes the effect on dilution is small. As the flow increases to

where the density of the combined effluent approaches that of the background, i.e.

the flow becomes neutrally buoyant, the dilution increases exponentially. It

becomes theoretically infinite as for this case the jet trajectory is then horizontal

and the jet centerline does not impact the seabed. For the three cases considered,

the additional volumes required to satisfy the dilution requirements of Table 12

and the volumes for neutral buoyancy are summarized in Table 14.

Table 14. Effect of added freshwater volumes

Case No.

Base flow

For 80% compliance Additional flow for neutral

buoyancy Dilution needed

Additional flow

(mgd) (mgd) (mgd) V6 9.9 38 4.8 5.5 V7 10.9 42 4.2 4.8 V8 12.9 47 2.3 2.8

Note that the actual volumes required to achieve the water quality

requirements would be slightly less than those given in Table 14 due to “in-pipe”

dilution by the added flow that will reduce the source concentrations.

39

7.3 Varied Port Flow

This mitigation technique varies the flow per port. This can be accomplished

either by holding the effluent temporarily in a storage basin and then pumping

intermittently at higher flow rates or by closing some of the open ports or opening

some of the closed ports. More port flow increases the jet exit velocity which

increases entrainment and increases the jet trajectory length thereby increasing

dilution. Because these strategies are essentially identical in terms of their effect

on dilution, only the former case is analyzed here. The results can also be used to

estimate the effects of opening or closing ports. There are presently 129 open ports

and 42 closed ports. So opening all ports would result in a reduction in the flow per

port by 25%. This case is included below.

The procedure is similar to that of the previous section. A pumping rate was

assumed and the internal hydraulics program was run. The highest and lowest port

flows and their diameters were obtained and dilution calculations run for both. The

lowest was chosen. For each pumping rate, the composition of the effluent, i.e. its

density, was assumed constant and equal to that of the base cases.

The resulting dilutions are plotted as a function of pumping rate in Figure 20

and summarized in Table 15. The effect of increased flow on jet trajectory predicted

by UM3 is shown for two typical cases in Figure 21.

Figure 20. Effect of pumping rate on dilution for flow cases V6, V7, and V8.

The increased jet velocity leads to a longer and flatter trajectory leading to

increased dilution at the impact point. However, as the flow increases, the port

opening also increases, offsetting the increased jet velocity.

The dilution increases quite slowly in response to increased flow rate and the

required dilutions cannot be achieved for flows below about 100 mgd, where the

head required would exceed 50 ft. Note that the effect on dilution of closing ports

is the same and can be readily estimated. For example, a doubling of the pumping

rate is equivalent to closing half the ports.

40

Table 15. Effect of added flow on dilution for selected scenarios

Case No.

Background density

Effluent Port conditions Dilution by Cederwall formula

Flow Density Flow Diam. Height Velocity Froude no. y/dF

(kg/m3) (mgd) (kg/m3) (gpm) (cfs) (in) (ft) (ft/s)

V6.20 1025.8 9.9 1041.1 54.3 0.121 1.70 4.0 7.7 29.5 0.96 16.6 V6.21 1025.8 12.0 1041.1 64.8 0.145 1.79 4.0 8.3 30.9 0.87 16.4 V6.22 1025.8 15.0 1041.1 75.1 0.167 1.86 4.0 8.9 32.6 0.79 16.5 V6.23 1025.8 20.0 1041.1 103.3 0.230 2.01 4.0 10.5 36.9 0.65 16.9 V6.24 1025.8 30.0 1041.1 160.5 0.358 2.21 4.0 13.4 45.2 0.48 18.3 V6.25 1025.8 40.0 1041.1 207.8 0.463 2.32 4.0 15.8 51.8 0.40 19.8 V6.26 1025.8 60.0 1041.1 308.3 0.688 2.52 4.0 19.8 62.5 0.30 22.1 V6.27 1025.8 100.0 1041.1 505.3 1.127 2.87 4.0 25.1 74.1 0.23 24.5 V7.20 1024.8 10.9 1036.5 58.3 0.130 1.74 4.0 7.9 34.2 0.81 17.4 V7.21 1024.8 12.0 1036.5 59.4 0.132 1.75 4.0 7.9 34.3 0.80 17.4 V7.22 1024.8 15.0 1036.5 76.0 0.169 1.86 4.0 9.0 37.7 0.68 17.7 V7.23 1024.8 20.0 1036.5 105.3 0.235 2.02 4.0 10.6 42.5 0.56 18.3 V7.24 1024.8 30.0 1036.5 161.4 0.360 2.21 4.0 13.5 52.0 0.42 20.1 V7.25 1024.8 40.0 1036.5 206.8 0.461 2.32 4.0 15.7 59.1 0.35 21.7 V7.26 1024.8 60.0 1036.5 307.3 0.685 2.52 4.0 19.8 71.4 0.27 24.5 V7.27 1024.8 100.0 1036.5 609.7 1.360 3.08 4.0 26.3 85.7 0.18 27.3 V8.20 1024.8 12.9 1030.6 66.5 0.148 1.80 4.0 8.4 50.6 0.53 21.3 V8.21 1024.8 15.0 1030.6 77.8 0.173 1.88 4.0 9.0 53.1 0.48 21.6 V8.22 1024.8 20.0 1030.6 105.9 0.236 2.02 4.0 10.6 60.4 0.39 22.9 V8.23 1024.8 30.0 1030.6 154.8 0.345 2.19 4.0 13.2 72.1 0.30 25.5 V8.24 1024.8 40.0 1030.6 205.3 0.458 2.32 4.0 15.6 82.8 0.25 28.0 V8.25 1024.8 60.0 1030.6 305.8 0.682 2.52 4.0 19.7 100.3 0.19 32.2 V8.26 1024.8 100.0 1030.6 500.8 1.117 2.86 4.0 25.0 119.7 0.14 36.8

41

Figure 21. Jet trajectories predicted by UM3 for flow cases V7.10 (red) and V7.14 (blue).

The reason for this seemingly paradoxical result is that the dilution for these

cases is primarily a result of jet-induced entrainment. For a pure jet (i.e. a flow with

neutral buoyancy) from a fixed orifice the flow, jet velocity, and entrained flow all

increase in direct proportion to each other. The dilution at any distance from the

nozzle, which is the ratio of the entrained flow to the source flow, therefore remains

constant and is dependent only on the nozzle diameter (Fischer et al. 1979). In

other words, increasing the flow for a pure jet does not increase dilution at a fixed

point.

Dilution at the seabed does increase for the present cases as the flow increases,

however, due to the longer jet trajectory before impacting the seabed as shown in

Figure 21. The effect is again mitigated, however, by the variable opening of the

nozzles: as the flow increases, the increase in jet velocity is much less than for a

fixed orifice. Similarly, reducing the flow per port by opening closed ports does

not result in a significant change in dilution. A fixed orifice would result in longer

trajectories and higher dilutions than found above, but the head required would

probably be prohibitive. It is clear that varying the flow per port either by pumping

at a higher rate or opening or closing ports is not an effective strategy for increasing

dilution.

7.4 Effect of Inclined Nozzles

7.4.1 Introduction

Diffusers for discharging dense effluents normally consists of nozzles that are

inclined upwards. The optimum angle to the horizontal is 60 (Roberts and Abessi,

2014) as this maximizes the jet path length and dilution at the impact point. Such

jets have been extensively studied and a typical flow image is shown in Figure 22.

As shown in the definition diagram, the jet reaches a terminal rise height yt and

42

then falls back to the seabed. The impact dilution, Si, interpreted here as the ZID

dilution, is where the jet centerline intersects the seabed.

LIF image Definition diagram

Figure 22. Laser Induced Fluorescence (LIF) image of a 60 jet and definition diagram.

Inclined jets can be achieved either by retrofitting the existing check valves

with upwardly inclined nozzles or by building a dedicated brine outfall and

diffuser. The analyses are similar and both are considered below. Also discussed is

the effect on dilution of positively buoyant effluents of retrofitting with inclined

jets.

7.4.2 Diffuser Retrofit

The nozzle designs with check valves are shown in Figure A-3 in Appendix A.

For the present analysis it was assumed that valves with similar hydraulic

characteristics (Figure A-2) were installed but inclined upwards at 60.

The dilution Si of a single 60 jet and the terminal rise height yt can be

estimated from (Roberts et al. 1997):

1.6i

j

S

F (22)

and

2.2t

j

y

dF (23)

where Fj is the jet densimetric Froude number (Eq. 2) and d the effective nozzle

diameter. These equations have been widely used for brine diffuser designs.

The dilutions and jet rise heights for all the base cases with dense discharges

were computed and the results are summarized in Table 16, which can be

compared to Table 7. The hydraulics was assumed to be the same as for the

horizontal jets.

It is apparent that the inclined jets increase dilution substantially. Dilution for

the base case, P2 pure brine, increases from 16:1 to 46:1. All of the required

SnSiyt

xi

xn

yLx

yo

Figure 1. Definition Sketch for Inclined Dense Jet.

43

dilutions for cases V6, V7, and V8 are also met and exceeded. The rise heights of

the jets are all less than 100 ft so the jets will always be submerged.

7.4.3 Dedicated Diffuser

A dedicated diffuser for brine discharges would probably consist of multiple

nozzles inclined upwards at 60 to the horizontal. (Not vertical as implied in the

settlement agreement as vertical jets result in impaired dilution). The nozzles

would be either distributed along the sides of the diffuser or clustered in rosette

risers as shown in Figure 23.

Figure 23. A brine diffuser with multiport rosettes.

The analysis for the diffuser would be similar to that for the inclined jets above,

but it is noted that the outfall and diffuser could be much shorter than the existing

outfall. Assuming that the outfall is only used for brine discharges (with all

secondary effluent through the MRWPCA outfall), the peak flow would be about

14 mgd, requiring an outfall diameter of around 24 inches. The outfall need not be

as long as the MRWPCA outfall as shoreline impact is not a major concern and

deep water is not required for dilution. For example (although further analyses

would be needed to optimize the outfall and diffuser lengths and nozzle details),

the rise height of the jets for the pure brine case in Table 13 is about 10 ft, so the

discharge could be into relatively shallow water. Costs for similar outfalls vary

widely, but Roberts et al. (2012) quote a median price range for installed outfalls

of 24 inch diameter of about $3,700 per meter with a range from $1,000 to $8,000

per meter.

44

Table 16. Effect of discharge through 60 nozzles

Case No.

Background conditions

Effluent conditions Port conditions

Equations 4 and 5 at ZID

Dilution Salinity

Rise height Salinity Density Salinity Density Flow Diam. Height Velocity Froude

no. y/dF At impact

Incr- ement

(ppt) (kg/m3) (ppt) (kg/m3) (gpm) (cfs) (in) (ft) (ft/s) (ppt) (ppt) (ft)

P1 0.80 998.8 P2 33.89 1025.8 58.23 1045.2 76.3 0.170 1.87 4.0 8.9 29.0 0.89 46.3 34.41 0.53 9.9 P3 33.34 1024.8 53.62 1041.2 75.0 0.167 1.86 4.0 8.9 31.4 0.82 50.3 33.75 0.40 10.7 P4 33.34 1024.8 50.32 1038.5 80.8 0.180 1.89 4.0 9.2 35.5 0.72 56.8 33.64 0.30 12.3 P5 33.34 1024.8 35.23 1026.4 117.8 0.263 2.07 4.0 11.2 120.3 0.19 192.5 33.35 0.01 45.7 P6 33.34 1024.8 24.24 1017.6 188.5 0.420 2.28 4.0 14.8 71.5 - - - - - V1 33.89 1025.8 58.23 1045.2 50.8 0.113 1.67 4.0 7.4 25.6 1.12 40.9 34.48 0.59 7.8 V2 33.89 1025.8 52.48 1040.5 54.3 0.121 1.70 4.0 7.7 30.1 0.94 48.1 34.27 0.39 9.4 V3 33.89 1025.8 47.78 1036.6 54.6 0.122 1.71 4.0 7.6 34.7 0.81 55.6 34.14 0.25 10.9 V4 33.34 1024.8 35.20 1026.4 77.9 0.174 1.88 4.0 9.0 102.0 0.25 163.1 33.35 0.01 35.1 V5 33.89 1025.8 18.75 1012.7 160.8 0.359 2.21 4.0 13.5 48.9 - - - - - V6 33.89 1025.8 53.27 1041.1 54.3 0.121 1.70 4.0 7.7 29.5 0.96 47.2 34.30 0.41 9.2 V7 33.34 1024.8 47.78 1036.5 58.3 0.130 1.74 4.0 7.9 34.2 0.81 54.7 33.61 0.26 10.9 V8 33.34 1024.8 40.52 1030.6 66.5 0.148 1.80 4.0 8.4 50.6 0.53 80.9 33.43 0.09 16.7 V9 33.89 1025.8 35.01 1026.1 77.8 0.173 1.88 4.0 9.0 260.5 0.10 416.7 33.89 0.00 89.8

V10 33.34 1024.8 20.67 1014.7 143.3 0.320 2.16 4.0 12.6 52.6 - - - - -

45

7.4.4 Effect of Inclined Nozzles on Buoyant Flows

Diffusers for positively buoyant discharges usually have horizontal nozzles (as

in the MRWPCA diffuser) as this maximizes jet trajectory and dilution and helps

promote submergence. Inclining the nozzles upwards may reduce dilution

somewhat. In order to investigate this effect, dilutions for the buoyant discharge

scenarios (P1, P6, V5, and V10) of Table 8 were recomputed but with 60 inclined

nozzles. The same hydraulic conditions were assumed. Dilution simulations were

done with the model UM3 only as NRFIELD assumes horizontal nozzles. The

results are summarized in Table 17.

Table 17. Summary of UM3 Dilution Simulations for Buoyant Effluent Scenarios with Horizontal and 60 Nozzles

Case No.

Flow rate

(mgd)

Effluent density (kg/m3)

Port diam. (in)

Ocean condition

Horizontal 60

Average dilution

Rise height (center-

line) (ft)

Average dilution

Rise height (center

line) (ft)

P1 19.78 998.8 2.00 Upwelling 191 58 184 62 P1 19.78 998.8 2.00 Davidson 327 100 (surface) 310 100 (surface) P1 19.78 998.8 2.00 Oceanic 240 82 247 91 P6 33.76 1017.6 2.25 Davidson 154 86 142 93 V5 28.77 1012.7 2.18 Upwelling 122 47 111 53

V10 25.85 1014.7 2.13 Davidson 195 100 (surface) 185 100 (surface)

For buoyant discharges of essentially freshwater into fairly deep water the

dilution is primarily effected by the buoyancy flux, so the source momentum flux,

and therefore the nozzle orientation, is relatively unimportant. This effect is shown

in the trajectories predicted by UM3 for case P1 in Figure 24. The trajectory lengths

are similar with a slightly higher rise for the inclined jets. The results show small

reductions in dilution of about 5% for this case as the trajectory reduction is offset

by the increased plume rise height. For case P1 with the Oceanic density profile,

the results actually imply a slight increase in dilution with the inclined nozzles due

to the increased rise height. For cases P6, V5, and V10 (buoyant discharges with

the density difference reduced due to blending with brine), the momentum flux is

slightly more important, but even here the dilution reduction is less than 10%

46

Figure 24. UM3 predicted trajectories for horizontal (red) and 60 inclined (blue) nozzles

for case P1 with upwelling density profile.

47

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Kikkert, G. A., Davidson, M. J., and Nokes, R. I. (2007). "Inclined Negatively Buoyant Discharges." J. Hydraul. Eng., 10.1061/(ASCE)0733-9429(2007)133:5(545), 133(5), 545-554.

Lee, J. H. W., and Tang, H. W. (1999) "Experiments of a Duckbill Valve (DBV) Jet in Coflow." Proc., IAHR Congress, Graz, Austria, August 1999.

Palomar, P., Lara, J. L., Losada, I. J., Rodrigo, M., and Alvárez, A. (2012a). "Near field brine discharge modelling part 1: Analysis of commercial tools." Desalination, 10.1016/j.desal.2011.11.037, 290(0), 14-27.

Palomar, P., Lara, J. L., and Losada, I. J. (2012b). "Near field brine discharge modeling part 2: Validation of commercial tools." Desalination,

48

10.1016/j.desal.2011.10.021, 290(0), 28-42.

Roberts, P. J. W., and Abessi, O. (2014). "Optimization of Desalination Diffusers Using Three-Dimensional Laser-Induced Fluorescence: Final Report. Prepared for United States Bureau of Reclamation." School of Civil and Environmental Engineering, Georgia Institute of Technology, January 22, 2014.

Roberts, P. J. W., Snyder, W. H., and Baumgartner, D. J. (1989). "Ocean Outfalls. I: Submerged Wastefield Formation." J. Hydraul. Eng., 115(1), 1-25.

Roberts, P. J. W., Ferrier, A., and Daviero, G. J. (1997). "Mixing in Inclined Dense Jets." J. Hydraul. Eng., 123(8), 693-699.

Roberts, P. J. W., Salas, H. J., Reiff, F. M., Libhaber, M., Labbe, A., and Thomson, J. C. (2010). Marine Wastewater Outfalls and Treatment Systems, International Water Association, London.

Shao, D., and Law, A. W.-K. (2011). "Boundary impingement and attachment of horizontal offset dense jets." Journal of Hydro-Environment Research, 10.1016/j.jher.2010.11.003, 5(1), 15-24.

SCCWRP (2012). “Management of Brine Discharges to Coastal Waters Recommendations of a Science Advisory Panel.” Southern California Coastal Water Research Project, Technical Report 694, March 2012.

SWRCB (2015). “Water Quality Control Plan Ocean Waters of California.” State Water Resources Control Board, California Environmental Protection Agency, Sacramento, California, Adopted May 6, 2015, Effective January 28, 2016.

Tian, X., and Roberts, P. J. W. (2003). "A 3D LIF System for Turbulent Buoyant Jet Flows." Expts. Fluids, 35, 636-647.

Tian, X., Roberts, P. J. W., and Daviero, G. J. (2004). "Marine Wastewater Discharges from Multiport Diffusers I: Unstratified Stationary Water." J. Hydraul. Eng., 130(12), 1137-1146.

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Trussell Technologies (2016) “Minimum Dilution Requirements.” Memorandum June 9, 2016.

Walter, R. K., Squibb, M. E., Woodson, C. B., Koseff, J. R., and Monismith, S. G. (2014). "Stratified turbulence in the nearshore coastal ocean: Dynamics and evolution in the presence of internal bores." Journal of Geophysical Research: Oceans, 10.1002/2014jc010396, 119(12), 8709-8730.

Webster, D. R., Roberts, P. J. W., and Ra'ad, L. (2001). "Simultaneous DPTV/PLIF measurements of a turbulent jet." Expts. Fluids, 30, 65-72.

Wygnanski, I. and Fiedler, H.E. (1969). "Some Measurements in the Self-Preserving Jet." Journal of Fluid Mechanics 38(3): 577-612.

49

APPENDIX A. DIFFUSER HYDRAULICS WITH CHECK VALVES

1. Introduction

The calculation procedure to predict the internal hydraulics and flow

distribution for diffusers with ports equipped with check valves is described below.

2. Check Valves

Typical check valves similar to those installed on the MRWPCA outfall are

shown in Figure A-1. As the flow though the valve increases, the opening area

increases, up to some limit. The valves attached to the MRWPCA outfall are four-

inch flange TideFlex TF-2, Series 35, Hydraulic Code 61. The characteristics of the

valves were provided by the manufacturer, TideFlex, Inc. and are shown in Figure

A-2. The main characteristics are total head loss, jet velocity, and effective opening

area as functions of flow rate.

Figure A-1. Typical “Duckbill” Check Valves

The relationship ( )jE f Q between the total head, E and flow Qj of Figure A2

over the flow range 50 to 300 gpm can be closely approximated by the linear

relationship:

0.020 0.276jE Q (A1)

where E is the head in feet, and Qj the flow rate in gpm. Similarly, the jet velocity

(in ft/s) can be approximated by:

5 2 24.71 10 6.49 10 4.28j j jV Q Q (A2)

The effective nozzle area Aj is then given by:

j

j

j

QA

V

50

and the diameter of an equivalent round nozzle, de by:

4 j

e

Ad

(A3)

Therefore, only the relationship between head and flow, Eq. A1, and flow and

velocity, Eq. A2, are needed and all other properties can be calculated from them.

Alternatively, the equivalent diameter can be calculated from the flow and head

assuming a discharge coefficient of one.

Figure A-2. Characteristics of 4” wide bill TideFlex check valve Hydraulic Code 61

51

3. Port Head Loss

According to the outfall design drawings (Figure A-3), the check valves are

fastened over existing two-inch diameter ports. The entrances to the ports are

gradually tapered bell mouths.

Figure A-3. Port and check valve arrangement

The head loss in the entrance from the diffuser to the port (entrance loss) can

be approximated by:

2

2d

f en

Vh x

g (A4)

where xen is an entrance loss coefficient and Vd the velocity in the diffuser pipe at

the port. The value of xen is not known exactly, but experiments on Tee fittings

reported by Ding et al. (2005) give loss coefficients for 6, 8, and 10 inch pipes with

branching flows. For the larger Tees the loss coefficients ranging from about 0.43

to 0.63 depending on the ratio of flow in the branch to the main pipe. We assume

a constant value of xen = 0.63. Because the port entrances are rounded, and most

of the head loss is in the jet velocity head, however, the results are not sensitive to

the value of xen.

Applying the Bernoulli equation to the flow through the port and valve and

combining Eqs. A1 and A4 yields for the head at the port:

2

Entrance loss + Valve loss

0.020 0.2762

den j

E

Vx Q

g

which can be rearranged as:

2 2 0.276

0.02en d

j

E x V gQ

(A5)

52

4. End Gate Port

The end gate of the diffuser has an opening at the bottom as shown in Figure

A-4. It is approximately 2 inches high in a 48-inch diameter pipe which

corresponds to an area of 25.8 in2, equivalent to a round opening of 5.73 inch

diameter.

Figure A-4. End gate opening.

We approximate the discharge though this opening as being equivalent to a

round sharp-edged orifice:

2DQ C A gE (A6)

where CD is the discharge coefficient assumed equal to 0.62, A is the opening area

and E the total head in the pipe just upstream of the end gate.

5. Diffuser and Pipe Head Loss

The head loss due to friction in the diffuser and outfall pipe can be

approximated by the Darcy-Weisbach equation:

2

2d

f

VLh f

D g (A7)

where L is the pipe length, D the pipe diameter, and f the pipe friction factor, given

by:

Re, kf f

D

(A8)

where Re is the Reynolds number, Re dV D where is the kinematic viscosity

and k the equivalent roughness height. The friction factor can be obtained from

the Moody diagram, but for computational purposes it is more convenient to

estimate it from:

2

0.9

0.255.74log

3.7 Re

fk D

(A9)

53

Generally accepted values of k for concrete pipe range from 0.012 to 0.12 inches.

We assume an average value of k = 0.066 inches.

6. Calculation Procedure

The calculation procedure is a problem in manifold hydraulics and is iterative,

similar to that described in described in Fischer et al. (1979) or Roberts et al.

(2010). It follows this procedure:

1. Assume a value of the head just upstream of the end gate, 1E . Then compute

the flow Q1 through the end opening from Eq. A6.

2. Compute the velocity in the diffuser pipe just upstream.

3. Compute the pipe friction factor from Eq. A9.

4. Compute the head in the diffuser pipe at the next upstream port from:

2

2 1 2dVs

E E f zD g

(A10)

where s is the port spacing, a o is the density difference between the

receiving water and the discharge, the receiving water density, and z the

height difference between the ports (positive if the inshore port is higher, i.e.

the diffuser is sloping downwards). Note that for a dense discharge, is a

negative number.

5. Compute the flow from the next upstream port, Q2, from Eq. 1.

6. Add the flows Q1 and Q2 to get the flow in the diffuser just upstream of the

port.

7. Repeat steps 2 through 6 for each port until the innermost port is reached.

Finally, the head loss in the rest of the outfall pipe up to the headworks is computed

from

2

+ density head2

dn

VLE E f

D g

where En is the head at the innermost port, n, and L is the outfall length

(excluding the diffuser).

The total flow and head loss in the outfall are not known ahead of time, so the

assumed head is Step 1 is then adjusted iteratively until the desired flow is

achieved. An Excel spreadsheet was written to accomplish these calculations. A

typical page from the spreadsheet for scenario P2 (pure brine) follows. For this

example, the flow per port increases in the offshore direction due to the negative

density head (dense brine discharge).

54

The total head for this case is essentially zero. This seemingly counterintuitive

result is because the density head essentially offsets the losses due to friction and

jet velocity.

Compute port flow distribution and total headloss with check valvesTideflex Series TF-2, 35

No. ports per riser, Nr = 1 Outfall pipe length, L (ft) = 10,274Port spacing, Sr (ft) = 8 Roughness height, ks (in) = 0.066

Depth of end port, Hend (ft) = 107 Gravity, g (ft2/s) = 32.2Slope of diffuser, Sl = 0.0110 Ambient density (kg/m3) 1025.8

Entrance loss coeff, xen = 0.63 Effluent density (kg/m3) 1045.2Density difference, Drho/rho = -0.019

Kinematic viscosity, nu (ft2/s) = 1.2E-05

Outfall friction headloss: 0.81 ftHead at end: 1.26 ft Diffuser headloss: 1.11 ft

Target flow: 14.0 mgd Density head: -1.81 ftComputed flow: 14.0 mgd Total outfall head: 0.11 ft

Pipe Jet Diam. Froude(in) n (ft) (ft) (ft) (gpm) (gpm) (gpm) (ft3/s) (ft/s) (ft/s) (in) (ft)

End port 1.26 457 457 457 1.0 0.1 5.7 5.73 10.51 48 1 0 107.0 1.26 76.3 76 533 1.2 0.1 9.0 1.87 29.1 3.1E+04 0.027 0.000

2 8 106.9 1.26 76.3 76 609 1.4 0.1 9.0 1.87 29.1 3.6E+04 0.026 0.0003 16 106.8 1.26 76.2 76 686 1.5 0.1 9.0 1.87 29.1 4.0E+04 0.026 0.0004 24 106.7 1.26 76.1 76 762 1.7 0.1 8.9 1.86 29.1 4.5E+04 0.026 0.0005 32 106.6 1.25 76.0 76 838 1.9 0.1 8.9 1.86 29.1 4.9E+04 0.025 0.0006 40 106.6 1.25 75.9 76 914 2.0 0.2 8.9 1.86 29.1 5.4E+04 0.025 0.0007 48 106.5 1.25 75.8 76 990 2.2 0.2 8.9 1.86 29.0 5.8E+04 0.025 0.0008 56 106.4 1.25 75.8 76 1065 2.4 0.2 8.9 1.86 29.0 6.2E+04 0.025 0.0009 64 106.3 1.25 75.7 76 1141 2.5 0.2 8.9 1.86 29.0 6.7E+04 0.024 0.00010 72 106.2 1.25 75.6 76 1217 2.7 0.2 8.9 1.86 29.0 7.1E+04 0.024 0.00011 80 106.1 1.24 75.5 76 1292 2.9 0.2 8.9 1.86 29.0 7.6E+04 0.024 0.00012 88 106.0 1.24 75.4 75 1367 3.0 0.2 8.9 1.86 29.0 8.0E+04 0.024 0.00013 96 105.9 1.24 75.3 75 1443 3.2 0.3 8.9 1.86 29.0 8.5E+04 0.024 0.00014 104 105.9 1.24 75.3 75 1518 3.4 0.3 8.9 1.86 29.0 8.9E+04 0.024 0.00015 112 105.8 1.24 75.2 75 1593 3.6 0.3 8.9 1.86 29.0 9.3E+04 0.024 0.00016 120 105.7 1.24 75.1 75 1668 3.7 0.3 8.9 1.86 28.9 9.8E+04 0.024 0.00017 128 105.6 1.23 75.0 75 1743 3.9 0.3 8.9 1.86 28.9 1.0E+05 0.024 0.00018 136 105.5 1.23 74.9 75 1818 4.1 0.3 8.9 1.86 28.9 1.1E+05 0.023 0.000

Frictionloss

Totalhead

Velocity Equivalentround port Reynolds

no.Frictionfactor

FlowPerport

Perriser CumulativeDepth

Inputted variables

Pipesegment

PipeID

Portnumber

Distancefromend

0

20

40

60

80

100

1336597129

Flow

per

por

t (gp

m)

Port no. Offshore

Port Flow Distribution

MWRPCA Hydraulics Negative

56

APPENDIX B. DENSITY PROFILES

The seasonally averaged density profiles assumed for modeling purposes are summarized below.

Depth (m)

Density (kg/m3)

Upwelling Davidson Oceanic 1 1025.1 1024.8 1024.8 3 1025.1 1024.8 1024.8 5 1025.1 1024.8 1024.8 7 1025.2 1024.8 1024.8 9 1025.2 1024.8 1024.8 11 1025.3 1024.8 1024.8 13 1025.4 1024.8 1024.9 15 1025.4 1024.8 1024.9 17 1025.5 1024.8 1024.9 19 1025.6 1024.9 1024.9 21 1025.6 1024.9 1025.0 23 1025.7 1024.9 1025.0 25 1025.7 1024.9 1025.0 27 1025.8 1024.9 1025.1 29 1025.8 1024.9 1025.1 31 1025.8 1024.9 1025.2 33 1025.9 1024.9 1025.2 35 1025.9 1024.9 1025.3

57

APPENDIX C. TURBULENCE EFFECTS ON ORGANISMS

Summary of lab and field data (and some models) regarding the effects of turbulence on organisms (from Foster et al.

2013).

Organism Shear

stress or turbulence

Method of generating

shear/turbulence

Magnitude of critical

shear/turbulence Effect Reference Additional notes

Sea urchin S. purpuratus larvae (3 day; prism)

Laminar shear

Couette flow1, short term (30 min)

No deleterious effect with ɛ ≤ 1 cm2/s3

Change in prey encounter rate

Maldonaldo and Latz (2011)

Neg eff cd be due to erosion of hydromech signal, or if local velocity faster than catch speed, reaction time. Mortality was 19% for the 0.1 cm2/s3, 22% for the 0.4 cm2/s3, and 53% for the 1 cm2/s3 flow treatments compared to 5% for the still control.

Couette flow Long term (8 days of 12 h on, 12 h off)

ɛ < 0.1 cm2/s3 Excessive

mortality

Sea urchin L. pictus larvae (3 day, 4 arm pluteus)

Laminar shear

Couette flow1, short term (30 min)


Change in prey encounter rate

Maldonaldo and Latz (2011)

Couette flow Long term (8 days of 12 h on, 12 h off)


Some mortality, but not much

Sea urchin S. purpuratus

Shear stress Couette flow (short term: 2 min)

No deleterious effect with ɛ < 200 cm2/s3

Fertilization and development to blastula

Mead and Denny 1995, Denny, Nelson and Mead 2002

Zebra mussel Dreissena polymorpha veliger

Turbulence Bubble plume for 24 hours, then 24 feed before mortality measured

Mortality increases when d* > 0.9 (eddy similar in size to larva (no sig eff when d*<0.9)

Mortality Rehmann et al. 2003

58

Organism Shear



shear/turbulence



dinoflagellate Alexandrium fundyense

Laminar shear

Couette flow for 1‐24 hours/day

Shear stress τ = 0.003 N/m2 ; ɛ = 10‐

5 cm2/s3 ; only 1 level

Growth rate decreased when exposed to τ for more than 2 hours/ day

Juhl et al. 2001

Growth rate = 0 when shear 12 h/d; negative when 16‐24 h/day

dinoflagellate Laminar Couette flow 1 h/d Shear stress τ = Growth rate Juhl et al. Most sensitive last hour of dark Alexandrium shear and 5–8 d and shaken 0.004 N/m2 (not decreased in 2000 phase, under lower light fundyense turbulence flasks quantified for both conditions

shaken flasks dinoflagellate Lingulodiniu m polyedrum.

Shear (steady and unsteady)

Couette flow; constant or changing speeds/direction; 2 h/d (change ev 2 min)

smallest ɛ = 0.04 cm2/s3; all had effect (very very high )

Growth rate decreased in all cases; often catastrophicall y (near 100%)

Latz et al. 2009

Unsteady flow had more of an effect than steady, even when mean was lower; poss mechanism: mechanical energy of the flow alters membrane biophysical properties, activates signal transduction pathway involving GTP, [ca2+]I, poss. Also involves cyclin‐dep kinases, as in endothelial cells

Copepod Acartia tonsa

Turbulence model Starts dropping at ɛ = 10‐3 cm2/s3

Decrease in prey capture success

Kiørboe and Saiz 1995

Copepods that set up feeding currents are largely independent of ambient fluid velocity for prey encounters, while ambush‐ preying copepods can benefit substantially


Turbulence Oscillating grid Saiz & Kiørboe 1995

Herring larvae Turbulence model Starts dropping at ɛ = 10‐3 cm2/s3



Cod larvae Turbulence model Starts dropping at ɛ = 10‐5 cm2/s3



59

Organism Shear



shear/turbulence



Cod Gadus

morhua (5‐6

mm)

Turbulence Oscillating grid; observations start after 10 min shaking

ɛ = 7.4 x 10‐4 cm2/s3)

Increase in “attack position rate” at all conc

MacKenzie and Kiørboe 1995

Cod benefit more from turb (pause‐travel)

Cod Gadus

morhua (8.7‐12.3 mm)

Turbulence ‐more intermitten t

Oscillating grid, observations start after a few min shaking

ɛ = .2, 2 x 10‐4 cm2/s3)

While encounter rate up, pursuit success down

MacKenzie and Kiorboe 2000

Decrease in pursuit success at higher ɛ; general downward trend with increased rel vel; smaller fish larvae affected more

Herring Clupea

harengus (8‐9

mm)

Turbulence Oscillating grid; observations start after 10 min shaking

ɛ = 7.4 x 10‐4 cm2/s3)

Increase in “attach position rate” only at low conc; v messy data

MacKenzie and Kiorboe 1995

Herring benefit less (cruise)

Juvenile rainbow trout and steelhead Oncorhynchus mykiss, Chinook salmon O. tshawytscha, American shad Alosa sapidissima

Shear stress Forced entry directly into submerged jet in flume having exit velocities of 0 to 21.3 m/s

No effect at 168/s 341/s; LC‐10 estimated at 495/s

Torn opercula, missing eyes

Nietzel et al. 2004

LC‐10 =affects 10% of population Juvenile fish 83‐232 mm fork length

Water flea Daphnia pulex

Turbulence Vibrating 0.5 cm grid

ɛ = 0.05 cm2/s3 (as compared to calm)

Heart rate increased 5‐ 27%

Alvarez et al. 1994

HR reflects increase in metabolic rate?

Copepod Calanus gracilis

Turbulence Vibrating 0.5 cm grid

ɛ = 0.05 cm2/s3 (as compared to calm)

Heart rate increased 93%

Alvarez et al. 1994

Other species too including crab larvae (increase HR 9%)


Turbulence Oscillating grid ɛ = 0.001 cm2/s3 (as compared to calm)

Decreases predator sensing ability

Gilbert and Buskey 2005

60

Organism Shear



shear/turbulence




Turbulence (field)

Boat wake (field); plankton tow inside/ outside wake

ɛ =310 cm2/s3 at a distance of 50 propeller diam. behind 20 mm diam, scale‐model boat propeller running at 3000 rpm

More dead inside wake (5‐ 25% increase, over 2‐12% background)

Bickel et al. 2011

Stain w neutral red


Mini stirrer w paddles (lab)

ɛ = 0, 0.035, 1.31, 2.24 cm2/s3

Bickel et al. 2011

ɛ = 0.035 cm2/s3 did not show negative effect

Various Turbulence (field)

Rapids (samples collected above and below rapids

ɛ = 3‐742 cm2/s3 Effects dep on species: sign. mortality in Littorina littorea, Mytilus edulis, and Aporrhais pespelicant

Jessop 2007 Mytilus membranipora, Electra pilosa, polychaete trochophores and Lamellaria perspicua had zero mortality

ɛ = energy dissipation rate (cm2/s3)

Couette flow: two concentric cylinders, outer one rotates shearing volume of fluid between cylinders at known rate

61

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